UNIVERSITY   OF   CALIFORNIA 

COLLEGE    OF    AGRICULTURE 
AGRICULTURAL   EXPERIMENT   STATION 

CIRCULAR  No.  227* 

June,  1921 

PLANT  DISEASE  AND  PEST  CONTROL 

BY 

W.  T.  HOENE  and  E.  O.  ESSIG 


ALFALFA 

Crown  Wart  =  Crown  Gall,  Urophlyctis  alfalfae  (Lag.)  Magn. ; 
Stem  Rot  or  Wilt,  Sclerotinia  libertiana  Fcl.  or  S.  trifoliorum  Ericks. — 
Crown  wart  appears  as  rounded,  irregular  tumors  near  the  surface  of 
tin1  ground,  but  has  no  connection  with  true  crown  gall.  Not  seriously 
destructive  in  California.  Stem  rot  is  due  to  a  fungus  similar  to  or 
the  same  as  that  causing  cottony  rot  of  lemons,  which  attacks  various 
other  plants  especially  leguminous  cover  crops.  Moist  and  cool 
weather  favor  it.    Stems  rot  off  near  the  crown  and  a  white  mold  with 

ttered  black  bodies,  often  as  large  as  popcorn  grains,  forms  on  or 
in  the  stems.  When  the  stand  becomes  too  poor,  plow  and  put  in 
some  other  crop  for  a  few  years.    Re-level  if  there  are  any  low  spots. 

Dodder  or  Love  Vine,  Cuscnta  sp. — Yellowish  threads  grow  up  and 
i  atwine  the  plants,  causing  serious  injury.  This  is  a  parasitic  plant 
with  minute  flowers  and  with  seeds  similar  in  size  to  alfalfa  seeds. 
Avoid  seed  in  which  dodder  occurs.  The  f  College  of  Agriculture  of  the 
University  of  California  maintains  a  laboratory  for  testing  seeds,  to 
which  samples  may  be  sent.  Small  patches  may  be  killed  by  mowing 
and,  when  dry,  burning  with  additional  material  or  kerosene.  After- 
wards resow  the  spot.     Badly  infested  fields  should  be  plowed  up. 


*  This  circular  is  a  revised  edition  of  Circular  No.  204,  Handbook  of  Plant 
Disease  and  Pest  Control,  by  E.  E.  Smith,  E.  O.  Essig,  and  George  P.  Gray,  which 
i3  out  of  print.  The  extensive  use  made  of  Circular  No.  204  and  the  need  for 
widening  its  scope  have  suggested  this  revision  and  re-issuance. 

The  authors  wish  to  acknowledge  with  appreciation  the  aid  of  E.  E.  Smith, 
E.  H.  Smith,  B.  A.  Eudolph,  H.  S.  Fawcett,  T.  Francis  Hunt,  J.  C.  Whitten,  H.  J. 
Quayle,  and  W.  "W.  Mackie,  and  the  Editorial  Committee  of  the  Experiment  Station, 
in  preparing  this  circular. 

t  After  January  1,  1922,  such  requests  should  be  directed  to  the  State  Depart- 
ment of  Agriculture,  Sacramento,  California,  as  at  about  that  time  a  laboratory 
will  be  established  by  the  State  Department  of  Agriculture  cooperating  with  the 
Bureau  of  Plant  Industry  of  the  U.  S.  Department  of  Agriculture. 


Z  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

In  the  drier  sections  it  is  reported  that  dodder  may  be  killed  by  keep- 
ing the  field  dry  for  a  time,  as  alfalfa  will  endure  more  drought  than 
dodder. 

Downy  Mildew,  Peronospora  trifoliorum  De  Bary. — The  upper 
parts  of  plants  turn  yellow,  the  leaves  curl  somewhat,  and  their  lower 
sides  show  a  fuzz  which  turns  violet.  Affected  plants  are  scattered. 
Remedies  apparently  have  not  been  tried  in  California. 

Rust,  Uromyces  striatus  Scr. ;  Leaf  Spot,  Pseudopeziza  medicaginis 
(Lib.)  Sacc. — Rust  shows  as  powdery  brown  dots  on  the  lower  side  of 
the  leaves,  and  leaf  spot  as  small  dark  spots,  rarely  exceeding  one- 
twelfth  inch  in  diameter.  Leaf  spot  is  the  more  common  of  the  two, 
and  is  often  so  abundant  as  to  cause  the  older  leaves  to  drop.  Not 
often  serious  or  persistent.  Worst  on  weak  plants  in  dry  soils  under 
unfavorable  growing  conditions.  Usually  disappears  after  cutting  and 
good  irrigation.  The  hay  is  valuable  for  orchard  mulch  if  too  rusty 
for  feed. 

Alfalfa  Caterpillar,  Eurymus  eurytheme  (Boisd.). — The  caterpil- 
lars are  about  one  inch  long  and  dark  green  in  color  with  a  distinct 
and  often  a  pale  white  or  yellow  line  on  each  side.  They  feed  on  the 
leaves  and  may  entirely  defoliate  the  plants.  The  yellow  butterflies 
may  be  seen  in  great  numbers  hovering  over  the  fields.  Cutting  as 
soon  as  the  caterpillars  appear  in  destructive  numbers,  followed  by 
irrigation,  is  the  best  method  of  control. 

Armyworms,  Cutworms,  Grasshoppers,  etc. — See  "General  Sub- 
jects. ' ' 

Clover  Seed  Chalcis  (Bruchophagus  funebris  How.). — The  small 
white  larva  of  this  insect  is  just  large  enough  to  fill  the  seed.  It  occurs 
in  sufficient  numbers  to  greatly  reduce  the  seed  crop  in  most  localities 
in  the  state.  Destroying  all  the  seed  heads  during  winter  and  the 
straw  after  threshing  will  greatly  reduce  the  infestation  for  the  next 
year. 

ALMOND 
Armillaria,  Crown  Gall,  Sour  Sap. — See  "General  Subjects." 
Shot-hole,  Coryneum  heijerinckii  Oud. ;  Rust,  Transchelia  punctata 
(Pers.)  Arth.  =  Puccinia  pruni. — Shot-hole  is  due  principally  to  the 
peach  blight  fungus.  It  causes  many  fruits  to  drop  and  kills  small 
spots  on  young  fruits  and  leaves.  The  tissue  of  the  expanding  leaves 
draws  away  from  the  dead  areas,  causing  them  to  drop  out  and  thus 
leave  holes.  Rust  develops  later  in  the  season  as  small,  rusty  brown 
dots  on  the  leaves  of  almonds,  apricots,  plums,  and  peaches.  Spray 
with  lime-sulfur  1-10,  just  as  the  buds  are  swelling. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  3 

Unfruitfulness. — Usually  due  to  frost  or  to  rain  at  blooming  time, 
or  to  lack  of  a  suitable  mixture  of  varieties  for  cross  pollination  (most 
varieties  are  self -sterile),  to  lack  of  bees  for  carrying  pollen,  or  to 
weakness  from  red  spider  or  other  injury  the  previous  year. 

California  Peach  Borer. — See  "Peach." 

Peach  Twig  Borer.— See  "Peach." 

Red  Humped  Caterpillar. — See  "Prune." 

Red  Spider  or  Almond  Mite,  Bryonia  pratensis  Garman. — The 
largest  orchard  mite,  nearly  the  size  of  a  pinhead  ;  brownish  or  greenish 
with  reddish  legs,  the  front  pair  as  long  as  the  body  and  much  longer 
than  the  other  legs.  The  bright  red,  globular  eggs  are  laid  in  great 
numbers  on  the  limbs  and  twigs  of  the  trees,  where  they  remain  through 
the  winter  and  hatch  in  the  spring.  Spray  the  trees  in  the  winter 
(January  and  February)  with  lime-sulfur  1-10  or  crude  oil  emulsion 
(Formula  18)  to  destroy  the  eggs.  To  control  the  mite  during  the 
growing  period  of  the  trees  apply  dry  sulfur,  sulfur  paste,  wettable 
sulfur  sprays  (Formula  13  or  14),  or  lime-sulfur  1-50  as  soon  as  the 
mites  appear  in  the  spring  and  as  often  as  necessary  during  the  summer 
and  fall. 

San  Jose  Scale. — See  "Apple." 

Combined  Spraying 
Lime-sulfur  spraying  when  the  buds  are  swelling  will  control  shot- 
hole  fungus  and  peach  twig  borer,  and  help  to  destroy  San  Jose  scale 
and  the  eggs  of  the  almond  mite.  Crude  oil  emulsions  will  also  destroy 
scale  insects,  almond  mite  eggs,  and  will  arrest  some  of  the  fungus 
diseases  when  applied  as  a  dormant  spray. 

APPLE 

Blight,  Bacillus  amylovorus  (Burr.)  De  T. — See  "Pear."  Remove 
all  worthless  apple,  pear,  and  quince  trees  near  apple  or  pear  orchards. 
Christmas  berry,  Cotoneaster,  and  related  wild  or  ornamental  plants 
should  be  watched  for  blight. 

Mildew,  Sphaerotheoa  leucotricha  (E.  &E.)  Salm.  &  8.  oxyaaanthae 
(De  C.)  De  B. — A  white  powdery  growth  covers  leaves  and  shoots, 
causing  stoppage  of  growth  and  distortion.  Where  abundant  the  tree 
is  weakened.  Especially  serious  in  foggy  sections.  Cut  out  mildewed 
twigs  as  thoroughly  as  possible  in  winter.  Use  lime-sulfur  for  scab 
spraying  or,  if  scab  is  not  serious,  use  sulfur  paste,  16  pounds  to  200 
gallons  of  water  (or  home-made  wettable  sulfur  spray,  Formula  13  or 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

14)  when  petals  are  falling.  Later  spraying  for  mildew  may  be  done 
with  the  same  material.  Sulfur  sprays  cause  injury  to  apple  trees  in 
some  sections. 

Sappy  Bark,  Polystictus  versicolor  (L.)  Fr. — Bark  puffs  up  in 
winter  about  wounds  and  dries  out  later,  becoming  loose  and  papery. 
Recurs  in  succeeding  winters,  causing  death  of  limbs  and  general 
breakdown  of  trees.  Caused  by  wood  decay  in  the  interior  of  the  tree. 
Avoid  large  wounds  or  protect  them  with  a  covering  of  asphalt.  See 
"Wood  Decay"  under  "General  Subjects." 

Scab,  Venturia  inequalis  (Cke.)  Wint.  =  Fusicladium. — Velvety 
dark  moldy  patches  on  young  fruit  and  sometimes  on  leaves  and  twigs, 
rough  corky  spots  on  mature  fruit,  with  distortion.  Spray  with 
Bordeaux  mixture  (Formula  9)  or  lime-sulfur  1-20,  just  as  blossoms 
open.    Again  with  lime-sulfur  1-35  when  petals  are  falling. 

Codling  Moth,  Cydia  pomonella  (Linn.). — The  common  white  or 
pinkish  worm  or  caterpillar  nearly  one  inch  long  is  found  inside  the 
fruit.  For  control,  spray  from  two  to  five  times  as  needed.  First 
spray  should  be  applied  as  the  petals  are  falling,  using  2%  pounds 
powdered  or  5  pounds  paste  arsenate  of  lead  to  100  gallons  of  water ; 
the  second  spraying  should  be  made  three  weeks  later  at  the  same 
strength.  The  remaining  applications  should  follow  as  needed,  but 
should  be  somewhat  weaker,  2  pounds  of  powdered  or  4  pounds  of 
paste  arsenate  of  lead  to  100  gallons  of  water.  Cover  with  a  fine,  fog- 
like spray.  For  a  spreader  use  1  pound  of  dry  billboard  paste  to  100 
gallons  of  spray  material.  (Also  see  "Spreaders"  in  "General  Sub- 
jects.") 

Flat-headed  Apple  Tree  Borer,  Chrysobotkris  mali  Horn. — The 
full  grown  larvae  or  borers  are  white  or  pale  yellow  and  vary  from 
one-half  to  three-quarters  of  an  inch  in  length.  The  portion  just 
behind  the  head  is  greatly  enlarged  and  flattened,  a  character  which 
is  responsible  for  the  common  name.  The  adult  beetles  lay  eggs  on 
sunburned  or  other  dead  areas  of  the  trunk.  "Whitewash  trunks  to 
prevent  sunburn  and  repel  egg-laying.  Avoid  injuries  and  wounds. 
Dig  out  borers  and  paint  with  asphaltum. 

Fruit  Tree  Leaf  Roller,  Archips  argyrospila  Walker. — The  eggs  are 
laid  in  small,  flat,  grayish  or  brownish  masses,  usually  on  the  new 
growth  near  the  tops  of  the  trees,  in  the  fall.  They  hatch  in  the  spring 
and  the  caterpillars  draw  the  leaves  together  into  compact  rolls  in 
which  they  live,  and  from  which  they  wriggle  violently  if  disturbed. 
When  mature  the  larvae  are  nearly  three-quarters  of  an  inch  long, 
deep  green,  with  the  head  and  thoracic  shield  dark  brown  or  black. 


CIRCULAR   227]  PLANT  DISEASE  AND  PEST   CONTROL  5 

The  most  satisfactory  means  of  control  is  directed  against  the  eggs, 
and  consists  in  the  use  of  a  miscible  oil  or  crude  oil  spray  (Formula  18) 
during  the  winter.  Great  care  must  be  taken  to  thoroughly  drench 
the  limbs  and  particularly  the  tops  and  outside  branches.  Some  relief 
may  be  had  during  the  summer  by  spraying  with  2  pounds  of  powdered 
or  4  pounds  of  paste  basic  arsenate  of  lead  to  100  gallons  of  water. 

Green  and  Rosy  Apple  Aphis,  Aphis  pomi  DeGeer  and  A.  mali- 
foliae  Fitch. — Both  of  these  aphids  are  easily  distinguished  by  their 
color  and  the  characteristic  curling  of  the  leaves,  caused  by  their 
nu'thod  of  attack.  Control  measures  are  difficult  and  must  be  thorough 
to  secure  satisfactory  results.  Late  dormant  lime-sulfur,  1-10,  applied 
just  before  the  buds  open,  gives  fair  results  in  killing  the  eggs,  but  it 
is  better  to  spray  from  the  time  of  the  bursting  of  the  buds  until  the 
leaf  buds  are  one-half  inch  long  with  nicotine  and  soap  (Formula  27), 
or  with  nicotine  and  distillate  emulsion  or  miscible  oil  (Formula  24), 
or  to  dust  thoroughly  with  5  or  6  per  cent  nicodust.  At  this  time  the 
young  stem-mothers  may  be  destroyed  as  they  hatch  from  the  eggs. 

Red  Humped  Caterpillar. — See  "Prune." 

San  Jose  Scale,  Aspidiotus  pemiciosus  Comst. ;  Oyster  Shell  Scale, 
Lepidosaphes  ulmi  (Linn.)  ;  and  Other  Scale  Insects. — The  scales  of 
the  first  are  circular  and  gray,  while  those  of  the  second  are  oyster- 
shaped  and  similar  in  color.  They  occur  on  all  parts  of  the  tree,  the 
first  causing  a  red  or  purplish  stain  on  the  bark  and  fruit.  For  the 
San  Jose  scale  alone,  spray  with  lime-sulfur,  1-10,  during  the  winter 
months.  For  a  mixed  infection  of  scales,  spray  preferably  with  crude 
oil  emulsion  (Formula  18),  or  with  distillate  emulsion  (Formulas 
21-23),  or  with  miscible  oil.  The  lighter  oil  sprays  are  not  so  efficient 
as  the  crude  oil  emulsion. 

Tent  Caterpillars  and  Cankerworms. — See  "General  Subjects." 

Tussock  Moths,  Hemerocampa  vetusta  (Boisd.)  and  Notolophus 
antiqua  (Linn.). — The  caterpillars  are  brilliantly  colored  and  clothed 
with  tufts  of  white  hair  on  the  dorsum,  with  a  single  long  black  tuft  at 
the  rear  and  two  in  front,  the  latter  being  responsible  for  the  name 
"horn  worms."  The  eggs  appear  as  white  flat  felty  masses  on  the  old 
cocoons  and  on  the  limbs  of  the  trees.  They  are  deposited  in  late 
summer  and  fall,  but  do  not  hatch  until  the  following  spring.  The 
female  moths  are  wingless  while  the  males  are  normally  winged.  Con- 
trol by  removing  the  egg  masses  during  the  winter  months.  Great 
numbers  of  the  caterpillars  may  be  jarred  from  the  trees  and  their 
reascending  prevented  by  applying  a  band  of  cotton,  wire  screen,  or 
tanglefoot  around  the  trunks.    Poison  sprays  are  of  little  use. 


b  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Woolly  Apple  Aphis,  Eriosoma  lanigera  (Hausm.). — Easily  dis- 
tinguished by  their  reddish  bodies  completely  covered  with  white 
woolly  wax.  During  the  winter  months  spray  with  distillate  emulsion 
(Formula  23),  miscible  oil,  or  carbolic  acid  and  distillate  emulsion 
(Formula  26a).  For  the  root  form,  expose  the  crown  of  the  roots  and 
pour  in  4  or  5  gallons  of  any  of  the  above  spray  mixtures  and  recover 
the  roots.  Nicotine  sulfate  (Formula  27)  is  also  effective,  or  refuse 
tobacco  stems  or  leaves  may  be  buried  in  the  soil  over  the  main  roots 
during  the  rainy  season.  Delicious  and  Northern  Spy  rootstocks  are 
somewhat  immune  and  are  often  used  to  repel  serious  attacks  of  this 
pest.    Of  the  two  stocks  the  former  is  more  vigorous  and  easily  grafted. 

Combined  Spraying 

1.  For  serious  infestations  of  scale  insects,  for  removal  of  moss  or 
lichens,  and  for  a  general  clean-up,  use  lime-sulfur  1-10  or  crude  oil 
emulsion  (Formula  18)  during  the  winter. 

2.  For  green,  rosy,  and  woolly  aphis,  use  distillate  emulsion  (Form- 
ula 23)  or  miscible  oils  just  as  the  buds  are  beginning  to  open.  .If 
only  the  first  two  are  present  and  scab  is  a  serious  pest,  substitute  late 
dormant  lime-sulfur  1-10.  This  will  assist  in  the  control  of  the  San 
Jose  scale,  if  present.  Combinations  of  oil  sprays  for  insects  with  lime- 
sulfur  or  Bordeaux  mixture  for  fungus  diseases  are  not  considered 
advisable. 

3.  For  codling  moth  and  scab  use  2  pounds  powdered  or  4  pounds 
paste  basic  arsenate  of  lead  to  100  gallons  of  1-35  lime-sulfur  when 
petals  are  falling.  For  mildew,  add  8  pounds  of  sulfur  paste  to  each 
100  gallons  of  the  above  and  one-half  pint  of  40  per  cent  nicotine 
sulfate  for  green  or  rosy  aphis.  For  later  infestations  of  codling  moth 
and  scab,  repeat  above,  following  recommendations  for  mildew  and 
aphis  if  these  need  attention. 

In  large  apple-growing  districts  obtain  advice  of  local  horticultural 
authorities  for  modifications  of  the  above. 

4.  For  summer  infestations  of  aphis  and  red  spiders,  a  combined 
nicotine  and  sulfur  dust  may  be  applied  to  great  advantage. 

APRICOT 

Armillaria,  Crown  Gall,  Sour  Sap,  Wood  Decay. — See  "General 
Subjects." 

Bacterial  Gummosis,  Bacterium  cerasi  Griffin. — Active  during 
moist  weather  of  winter  and  spring.  Attacks  buds,  twigs,  branches, 
and  trunks.     Copious  turbid  or  colored  gum  appears.     Affected  bark 


CIRCULAR  227]  PLANT  DISEASE  AND  PEST  CONTROL  7 

when  cut  into  shows  moist  gumming  rot.  Cut  out  diseased  bark  and 
disinfect  wounds  and  tools  as  for  pear  blight  (see  " Pear  ") .  After  the 
first  rains  the  orchard  should  be  frequently  inspected  and  all  cankers 
treated  promptly  to  stop  their  spreading.  Summer  treatment  is  of 
doubtful  value,  though  gum  may  continue  to  flow. 

Black  Heart. — Certain  branches  die  back  suddenly  in  summer  with 
leaves  attached  and  the  wood  of  affected  twigs  dark-streaked  far  back 
into  the  tree.  Peaches,  prunes,  and  almonds  are  sometimes  affected. 
Avoid  excessive  irrigation,  severe  cutting  back,  or  otherwise  promoting 
too  succulent  growth.  Make  conditions  as  normal  as  possible ;  trees 
usually  outgrow  the  trouble.  Investigations  now  under  way  will  be 
fully  published  later. 

Brown  Rot,  Blossom  Blight,  Gumming  Twig  Blight,  Monilia  Rot 
of  Ripe  Fruit,  Sclerotima  cinerea  (Bon.)  Schr. ;  Green  Rot  and  Twig 
Blight,  Sclerotinia  Ubertiana  Fcl. — Blossoms  after  opening  are  killed 
rapidly  during  damp  weather,  and  older  twigs  may  die  back  from  a 
few  inches  to  several  feet  as  the  result  of  girdling  by  the  fungus  work- 
ing down  the  fruit  spurs.  Small  gray  powdery  tufts  of  spores  usually 
appear  on  killed  parts  immediately  and  again  the  following  season. 
Clear  amber  gum  exudes  along  the  boundary  of  dead  and  living  tissue. 
Ripening  fruit  rots  rapidly  from  slight  injuries,  the  rotten  fruits  be- 
coming covered  with  a  copious  ashy-gray  powder.  In  clusters  the 
disease  passes  directly  from  diseased  to  healthy  fruit.  All  stone  fruits 
are  affected.  During  fall  or  winter  remove  the  blighted  twigs  and 
mummies.  The  period  for  effective  control  by  sprays  is  very  short. 
Spray  with  lime-sulfur  1-10  when  the  buds  are  in  full  pink  or  with 
standard  Bordeaux  when  they  are  about  one-fifth  in  bloom.  For  more 
thorough  control  apply  lime-sulfur  or  Bordeaux  twice  between  the 
time  when  the  buds  begin  to  swell  noticeably  and  the  time  when  the 
bloom  is  about  one-fifth  out.  Never  use  lime-sulfur  on  apricots  at  any 
period  after  the  fruit  has  set.  Crude  oil  emulsion,  made  with  lime- 
sulfur  1-10  instead  of  water,  may  be  applied  in  the  pink.  Emulsions 
made  with  soap  and  miscible  oils  with  lime-sulfur  are  dangerous  on 
apricots  at  any  time.  Lime-sulfur  injury  consists  in  yellowing  of  the 
foliage,  stunting  of  the  fruit,  and  disfigurement  of  the  fruit  by  sedi- 
ment. There  appears  to  be  no  way  to  prevent  the  occasional  occur- 
rence of  sulfur  injury  with  any  sulfur  spray  and  Bordeaux  is  appar- 
ently as  effective  a  fungicide. 

Bud  Blight,  Shot  Hole,  Fruit  Spot,  Peach  Blight,  Coryneum  beije- 
rinckii  Oud. — Buds  are  blackened  and  killed  during  winter;  spots 
killed  in  the  opening  leaves  fall  out  and  leave  holes,  and  small  red 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

spots  with  light  centers  are  formed  in  the  young  fruit.  Spray  with 
Bordeaux  or  lime-sulfur  between  November  15  and  December  15,  and 
repeat  in  spring  when  buds  are  showing  pink.  See  "Almond"  and 
"Peach." 

Frost  Scabs,  Fruit  Cracking  and  Red  Specking,  Failure  of  Flower 
Buds  to  Open  on  Strong  Shoots,  Unfruitfulness  of  Some  Varieties. — 

Due  to  climate  or  obscure  causes,  and  often  confused  with  fungus 
diseases. 

Scab,  Cladosporium  carpophylum  Thiim. — Sooty  patches  to  one- 
half  inch  in  diameter  and  often  confluent  form  on  the  fruit,  causing 
drying  and  cracking.    Sprays  for  brown  rot  will  probably  control  this. 

Branch  and  Twig  Borer,  Polycaon  confertus  Lee. — A  small  elong- 
ated brown  beetle,  one-quarter  of  an  inch  long,  which  bores  clean 
round  holes  at  the  bases  of  buds,  fruit  spurs,  and  in  the  forks  of  small 
twigs.  Often  makes  necessary  severe  pruning.  The  insect  breeds  in 
dead  oaks  and  prunings  of  fruit  and  other  trees.  Clean  up  and  burn 
dead  brush  and  prunings  around  orchards. 

Brown  Apricot  Scale,  Lecanium  corni  Bouche,  and  Black  Scale, 

Saissetia  oleae  (Bern.). — Immature  scales  of  both  species  are  brown 
or  grayish,  the  latter  having  a  distinct  "  H  "  on  the  back.  They  mature 
in  May  and  June  and  are  nearly  hemispherical ;  the  former  is  smooth 
and  brown  and  the  latter  black.  Control  is  directed  against  the  im- 
mature winter  forms  which  occur  on  the  new  growth.  Spray  the 
trees  when  dormant,  December  to  February,  with  crude  oil  emulsion 
(Formula  18),  distillate  emulsions  (Formulas  20-23),  and  miscible 
oils,  all  of  which  give  excellent  control  for  both  of  these  scales.  Thor- 
oughness of  application  is  necessary.  (See  Circular  No.  224,  Calif. 
Agr.  Exp.  Sta.,  Univ.  Calif.,  Dec,  1920.) 

California  Peach  Borer. — See  "Peach." 

Cankerworms. — See  "General  Subjects." 

Fruit  Tree  Leaf  Roller.— See  "Apple." 

Peach  Twig  Borer.— See  "Peach." 

Red  Humped  Caterpillar. — See  "Prune." 

Shot  Hole  Borer,  Xyleborus  xylographies  Say  and  Bark  Beetle, 

Eccoptogaster  rugulosus  (Ratz.). — Very  small  beetles  boring  into  the 
sapwood  and  heartwood  of  various  fruit  trees,  preferring  usually  those 
not  in  the  best  of  health.  White  larvae  of  the  latter  may  be  found 
during  the  winter  months  in  sapwood,  where  they  may  entirely  girdle 
the  trees.  Keep  the  trees  growing  vigorously ;  prune  out  and  burn  all 
dead  wood ;  destroy  all  infested  branches  immediately. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  9 

Combined  Spraying 
Dormant  strength  lime-sulfur  (1-10)  applied  just  as  the  buds  are 
beginning  to  open,  as  recommended  for  fungus  diseases,  will  also  con- 
trol the  peach  twig  borer,  remove  moss,  and  give  the  trees  a  general 
clean  up.  See  "Brown  Rot"  for  sulfur  injury  and  for  crude  oil 
emulsion  added  to  lime-sulfur. 

ASPARAGUS 

Rust,  Puceinia  asparagi  D.  C. — Minute  yellowish  blisters  or  sori 
appear  on  leaves  and  stems ;  these  rupture  and  become  rrst-colored  and 
dusty  and  later  black.  Plants  become  pale  and  bare  and  are  much 
weakened  for  succeeding  crops.  Keep  down  all  volunteer  growth  in 
ami  about  the  fields.  After  cutting  stops,  irrigate  and  cultivate  to 
secure  vigorous  growth,  and  in  about  three  weeks  dust  with  sulfur 
while  the  dew  is  on,  or  spray  with  resin-Bordeaux  (Formula  10a)  or 
lime-sulfur  containing  fish-oil  soap  for  a  spreader,  or  with  fish-oil  soap 
and  dust  with  sulfur  while  still  wet.  Repeat  once  or  twice,  according 
to  tlic  severity  of  the  disease  in  the  vicinity.  For  young  fields,  dust 
repeatedly  with  sulfur  as  above  to  prevent  infection,  beginning  when 
the  tops  first  fully  feather  out. 

Asparagus  Beetle,  Crioceris  asparagi  Linn. — The  beetles  are  slen- 
der,  one-fourth  of  an  inch  long,  metallic  blue-black  with  red  and  yellow 
markings.  The  larvae  are  dull  brown  or  olive  green  with  black  head 
and  legs.  They  feed  in  great  numbers  upon  the  seedlings.  Control 
by  clean  culture,  by  cutting  and  burning  seedlings,  or  by  spraying 
them  with  nicotine  soap  spray  (Formula  24  or  27).  A  6  per  cent 
nieodust  also  gives  quite  efficient  control. 

Garden  symphylid,  Scutigerella  calif  or  nica  (Woodw.). — These  are 
small,  white,  centipede-like  animals,  scarcely  more  than  one-quarter 
of  an  inch  long.  They  live  in  the  damp  soil  in  great  numbers  and  often 
seriously  damage  the  young  asparagus  tips  before  they  reach  the  sur- 
face of  the  soil.  Clean  culture,  winter  flooding,  and  crop  rotation  are 
the  best  control  suggestions. 

AVOCADO 

Pythiacystis  Canker,  Pythiacystis  citrophthora  S.  &  S. — Limb  and 
trunk  cankers,  resembling  gummosis  of  lemon,  but  the  gummy  exudate 
hardens  into  a  granular  whitish  mass.  Treat  as  for  citrus  gummosis 
(see  "Citrus  Fruits"). 

Soil  or  Drainage  Injury. — Certain  sickly  conditions  apparently 
caused  by  uneven  moisture  due  to  hardpan  or  other  soil  defects.    Trees 


10  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

apparently  sensitive  to  waterlogging  of  soil  and  with  poor  recuperative 
power  after  such  injury. 

Branch  and  Twig  Borer. — See  "Apricot."  Sap  collecting  in  the 
burrows  produces,  on  evaporation,  white  powdery  masses  over  the 
entrances,  completely  concealing  them. 

Fruit  Tree  Bark  Beetle.— See  "Apricot." 

Spanish  Red  Scale,  Chrysomphalus  dictyospermi  Morgan. — A  pale 
brown,  circular  scale,  infesting  all  parts  of  the  tree  and  serious  in 
greenhouses,  but  as  yet  not  adapted  to  orchard  conditions.  Control 
by  fumigation  with  hydrocyanic  acid  gas. 

Thrips:  Lean  Thrips,  Heliothrips  fasciatus  Perg.,  and  Greenhouse 
Thrips,  Heliothrips  haemorrhoidalis  Bouche. — See  "Prune."  These 
insects  attack  the  leaves  and  fruit,  causing  a  shiny,  hard  discolored 
surface  which  has  a  tendency  to  check,  or  crack,  and  which  is  covered 
with  numerous  fine  specks  of  excrement. 

BARLEY— See  "Grain" 

BEAN 

Anthracnose,  Collet otrichum  lindemuthianum  (S.  &  M.)  B.  &  C. — 
Spots  on  leaves,  stems,  and  pods,  up  to  two-fifths  inch  in  diameter, 
dark-colored,  usually  with  a  red  border  and  pinkish  in  the  center. 
Very  rare  and  unimportant  in  California. 

Mildew,  Erysiphe  polygoni  D.  C. — Forms  a  powdery  white  cover- 
ing over  green  parts  of  the  plants;  later  brownish.  May  seriously 
reduce  the  vitality  of  the  plants.  Dust  with  sulfur  at  first  appearance, 
or  with  sulfur  nicodust  if  thrips  or  aphis  are  present. 

Rust,  Uromyces  appendiculatus  (Pers.)  Link. — Rust-colored  spore 
masses  or  sori  of  pinhead  size  break  through  the  lower  surface  of  the 
leaf,  with  yellow  spots  above.  Affected  leaves  are  weakened  and  pro- 
duction decreases.  Dust  with  sulfur  at  first  sign  of  the  disease  and 
keep  the  surface  of  the  soil  dry  by  cultivation. 

Wilt  or  Stem  Rot,  Corticium  vagurn  B.  &  C.  =  Rhizoctonia,  and 
Fusarium  sp. — Many  plants  die  while  small  from  rot  near  the  surface 
of  the  soil,  others  wilt,  at  different  stages.  Prepare  the  soil  very  thor- 
oughly, plant  as  late  as  possible,  avoiding  cold  and  wet  weather.  Save 
seed  from  strong,  well  matured  plants. 

Bean  Aphis,  Aphis  rumicis  Linn. — A  small  black  louse  collecting 
in  great  numbers  on  the  leaves  and  tender  tips.  Use  5  per  cent  nico- 
dust or  spray  with  nicotine  paste  spray  (Formula  27a). 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  11 

Bean  Thrips,  Heliothrips  fasciatus  Perg. — A  small  dark  thrips  with 
black  and  white  wings.  The  larvae  are  white  and  pinkish  and  appear 
in  great  numbers  on  the  lower  surface  of  the  leaves.  Treatment  the 
same  as  for  bean  aphis. 

Bean  Weevil,  Acanthoscelides  obtectus  Say. — The  adults  are  short, 
robust,  and  about  one-eighth  inch  long.  The  color  varies  from  gray 
to  brown  with  pale  spots  on  the  dorsum.  The  larvae  work  within  the 
stored  beans,  from  which  the  adults  emerge  through  round  holes. 
Breeding  continues  in  storage.  Fumigate  in  storage  with  carbon 
bisulfide,  10  to  30  pounds  to  every  1000  cubic  feet  of  air  space,  the 
amount  depending  upon  the  tightness  of  the  container.  The  temper- 
ature should  be  above  70°  F.  to  secure  satisfactory  control  by  killing 
eggs,  larvae,  and  adults. 

Garden  Nematode. — See  "General  Subjects."  Black  eyes  and 
Teparys  are  more  resistant  than  other  beans,  but  are  sometimes  badly 
infested. 

Red  Spider  or  Two-Spotted  Mite,  Tetranychus  telarius  Linn. — A 
very  small  yellow,  pale  green  or  reddish  mite,  often  with  two  large, 
or  m\  small,  dark  spots  on  the  body.  Feeds  on  the  under  side  of  leaves 
and  often  spins  a  considerable  web.  If  possible  keep  the  beans  well 
irrigated  and  cultivated  and  in  good  healthy  condition.  Begin  sulfur- 
ing  as  soon  as  the  mites  appear  and  continue  throughout  the  summer, 
using  75  parts  of  dry  sulfur  to  25  parts  finely  ground  dry  hydrated 
lime. 

Wireworms. — See  "General  Subjects." 

BEET 

Curly-leaf  =  Curly-top  or  Blight. — Transmitted  by  the  beet  leaf 
hopper,  Eutettix  tenella  Baker.  Leaf  margins  curl  inward  or  rarely 
outward  and  are  much  dwarfed  and  deformed;  plants  are  stunted  and 
easily  killed  by  drought  and  heat ;  young  leaves  show  transparent  vena- 
tion (a  clearing  of  the  ultimate  leaf  vein  branches),  and  a  warty  con- 
dition usually  develops  on  the  backs  of  veins  on  old  leaves.  Roots  often 
become  hairy  and  show  dark  rings  in  cross-section.  In  the  cool  districts 
subject  to  ocean  fogs,  the  insects  do  not  reproduce  abundantly  and  the 
disease  when  established  is  less  injurious.  Beets  in  all  other  parts  of 
the  Pacific  slope  and  of  the  Rocky  Mountains  are  liable  to  injury,  but 
in  certain  regions  have  been  observed  to  suffer  less  than  in  others. 
Early  planting  to  bring  the  beets  to  a  good  size  before  the  spring  inva- 
sion of  the  insects  from  plains  and  foothills  is  generally  successful 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

except  in  years  following  early  fall  rains,  which  bring  up  filaree  and 
other  vegetation  and  cause  a  large  number  of  insects  to  winter  in  the 
cultivated  area.  Blighted  "stechlings"  do  not  produce  seed  success- 
fully, although  the  symptoms  many  not  always  be  apparent. 

The  sugar  beet  leafhopper,  Eutettix  tenella  Baker  referred  to  above 
is  wingless  in  the  immature  form  and  winged  when  full  grown.  The 
adults  average  about  one-fourth  inch  in  length.  The  color  varies  with 
the  season ;  those  of  the  spring  brood  being  pale  green ;  those  of  the 
summer  brood  are  cream  colored ;  while  the  winter  generations  are 
dark  colored  with  dark  markings  on  the  wing  covers.  The  insects  are 
to  be  found  chiefly  on  the  under  surfaces  of  the  leaves  or  between  the 
stems  near  the  crown  and  produce  the  characteristic  "curly-leaf" 
described  above. 

Downy  Mildew,  Peronospora  schactii  Fcl. — Inner  leaves  become 
curled,  dwarfed,  and  covered  below  with  a  violet  mildew.  Develops 
in  moist  weather.    Remove  affected  plants  and  destroy. 

Rust,  Uromyces  betae  (Pers.)  Kuhn;  Leaf  Spot,  Cercospora  beticola 
Sacc. — Rust  shows  as  brownish  pustules  or  sori  of  pinhead  size  on  the 
leaves,  and  leaf  spots  as  dead  gray  spots,  mostly  one-sixteenth  inch  in 
diameter  or  smaller,  with  borders  of  brown  or  purple.  No  treatment 
needed. 

Seedling  Root  Rot,  Corticium  vagum  B.  &  C.  =  Rhizoctonia,  and 
Fusarium  sp. — Roots  are  injured  and  become  misshapen  and  forked; 
plants  are  delayed  or  stunted  or  die.  Make  the  soil  conditions  as  favor- 
able as  possible  for  vigorous  growth.    Replant  if  the  stand  is  too  thin. 

Armyworms  and  Cutworms. — See  "General  Subjects." 

Beet  or  Spinach  Leaf -miner. — See  "Spinach." 

Grasshoppers. — See  "General  Subjects." 

Nematodes.— See  "General  Subjects."  The  beet  is  attacked  by 
two  species,  the  garden  nematode,  Heterodera  radicicola  Greef,  which 
produces  galls  on  a  number  of  plants,  and  the  beet  nematode,  H. 
schachtii  Schmidt,  which  is  confined  to  sugar  beets  and  does  not  pro- 
duce galls. 

Wireworms. — See  "General  Subjects."  For  the  sugar  beet  wire- 
worm,  Limonius  calif  amicus  (Mann.),  plow  in  fall  to  destroy  the 
pupae.  Plant  early  and  practice  clean  culture.  Trap  the  adults  by 
means  of  piles  of  straw  and  burn  in  late  fall  or  winter. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  13 

BUSH  FRUITS  (Blackberry,  Loganberry,  Raspberry) 
Crown  Gall,  Bacterium  tumefaciens  Sm.  &  T. — See  "General  Sub- 
jects." 

Fruit  Mold,  Botrytis  and  Other  Fungi. — Avoid  mixing  bruised  or 
moldy  berries  with  good  ones. 

Leaf  Spot,  Septoria  rubi  West,  Cane  Blight,  Leptosphaeria  conio- 
thyrium  Sacc.  =  Coniothyrium. — The  former  shows  small  light-colored 
dead  spots  with  brown  and  reddish  borders.  The  second  causes  dead 
areas  on  the  canes,  which  are  girdled  and  die.  Cut  out  and  burn  all 
affected  parts  in  the  fall.  Spray  with  lime-sulfur  or  Bordeaux  during 
the  dormant  season.  Give  proper  irrigation  and  cultivation.  Renew 
old  plantings.  Sometimes  confused  with  anthracnose,  which  has  not 
been  identified  in  California. 

Orange  Rust,  Gymnoconia  inter stitialis  (Schlect.)  Lagerh. — Bright 
orange  spores  cover  the  lower  surface  of  leaves.  Cut  off  the  diseased 
plants  below  the  surface  of  the  ground  and  burn.  Spray  with  Bor- 
deaux mixture  to  prevent  infection  of  healthy  plants. 

Raspberry  Horntail,  Hartigia  cressoni  (Kirby). — The  small  white 
larvae  are  shaped  somewhat  like  the  letter  "S"  and  when  mature  are 
nearly  one  inch  long.  They  first  attack  the  tender  tips  of  the  new 
canes  and  after  girdling  them  and  causing  wilting  they  work  down 
the  pith  to  the  roots,  where  they  spend  the  winter.  Cut  off  the  young 
tins  as  soon  as  wilting  is  noticed  so  as  to  kill  the  larvae  before  they 
reach  the  roots.  Remove  all  dead  canes  in  winter,  using  care  to  dig 
out  the  borers  at  that  time. 

Rose  Scale,  Aulacaspis  rosae  (Bouche). — A  pure  white  scale 
often  found  in  great  numbers  at  the  bases  of  the  old  canes.  Spray  in 
winter  with  distillate  emulsion  (Formula  23)  or  with  miscible  oil. 
Prune  out  old  canes  every  year,  because  infestation  spreads  from  them. 
Serious  only  where  pruning  is  not  practiced  every  year.  Lime-sulfur 
used  as  a  fungicide  gives  some  control. 

CABBAGE 

Armyworm  and  Cutworms. — See  "General  Subjects."  Scatter 
poison  bran  (Formula  4)  broadcast  over  the  ground  and  plants  in  the 
evening. 

Cabbage  Aphis,  Aphis  brassicae  Linn. — A  small  green  aphis  en- 
tirely covered  with  fine  whitish  powdery  wax.  Is  best  controlled  by 
liberal  and  repeated  applications  of  nicotine-distillate  spray  (Formula 
24)  or  of  nicotine  soap  (Formula  27).  Nicodust  gives  only  partial 
control. 


14  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Cabbage  Worm,  Pontia  rapae  (Linn.). — A  small  green,  velvety 
worm,  one  inch  long  when  mature,  which  feeds  upon  the  leaves  and 
destroys  the  heads.  The  adults  are  white  butterflies  with  dark  spots 
on  the  front  wings.  Young  cabbage  plants  may  be  protected  by  using 
arsenate  of  lead,  1  pound  of  powder  or  2  pounds  of  paste,  to  50  gallons 
of  water.  This  should  not  be  applied  after  the  heads  are  formed  be- 
cause of  possible  poisoning  of  humans.  Later  control  may  be  accom- 
plished by  applying  a  nicotine  soap  spray  (Formula  27) .  A  5  per  cent 
nicodust  also  gives  very  good  control  when  liberally  applied. 

Cabbage  Root  Maggot,  Phorbia  brassicae  Bouche. — The  small 
white  maggots,  one-fourth  inch  long,  are  found  tunneling  the  roots 
and  they  often  entirely  destroy  them.  In  transplanting,  place  tarred 
paper  shields  around  the  bases  of  the  plants  to  prevent  infestation,  or 
spray  with  carbolic  acid  emulsion  (Formula  26)  as  a  repellent.  Plow 
and  work  the  ground  thoroughly  in  winter  and  spring  to  expose  and 
destroy  the  pupae. 

CANTALOUPE.    See  Melon 
CASABA.    See  Melon 

CELERY 

Blight,  Cercospora  apii  Fr.  and  Septoria  petroselini  Desm. — Large 
or  small  dead  spots  appear  on  the  leaves  and  leaf  stalks,  especially 
after  cutting,  and  rapid  deterioration  follows.  Spray  repeatedly  with 
Bordeaux  (Formula  9),  especially  in  moist  weather,  commencing  in 
the  seed  bed. 

Aphids,  Rhopalosiphum  persicae  (Sulz.)  and  Siphocoryne  capreae 
(Fab.). — Green  aphids  attacking  the  stems  and  leaves  of  the  plants. 
Spray  with  nicotine  soap  (Formula  27)  or  dust  with  5  per  cent  nico- 
dust. 

Celery  Caterpillar,  Papilio  zolicaon  Boisd.— The  caterpillars  are 
beautifully  marked  green,  black  and  orange,  and  feed  upon  the  leaves. 
Hand  pick  or  spray  with  arsenate  of  lead  not  later  than  three  weeks 
before  harvest  (Formula  2). 

CHERRY 

Armillaria,  Wood  Decay,  Sour  Sap.— See  " General  Subjects." 
Gummosis,  Die-back.— See  "General  Subjects."     Usually  due  to 
shallow  soil  or  too  much  water  or  summer  drought.     Some  forms  of 


ClKCLLAK   12:27]  PLANT  DISEASE  AND  PEST  CONTROL  15 

guminosis  are  caused  by  specific  bacteria  (see  "Apricot").  Cut  out 
girdled  branches  below  diseased  parts  and  cut  out  affected  areas  of 
bark.     Sterilize  as  in  pear  blight.     See  also  "Wound  Treatment." 

Leaf  and  Fruit  Spot,  Coryneum  beijerinckii  Oud. — See  "Apricot," 
"Peach,"  "Almond." 

Leaf  Spot,  Coccomyces  hiemalis  Higgins. — Tiny  spots  covering 
most  of  the  leaf  surface  and  becoming  fused  at  the  lower  edge.  Under 
side  shows  whitish  coating  of  spores.  Not  serious  as  yet.  Controlled 
in  the  East  by  Bordeaux  mixture,  5-5-50  or  lime-sulfur  1-50  adding 
iron  sulphate  1*4  pounds,  or  dusting  with  sulfur.  Applications  as 
follows:  (1)  when  the  fruit  is  free  from  the  calyx,  (2)  two  weeks  later, 
(3)  just  after  the  fruit  is  picked. 

Black  Cherry  Aphis,  Myzus  cerasi  Fabr. — A  shiny  black  aphid  with 
long  honey  tubes ;  appearing  in  spring  and  early  summer  and  causing 
severe  curling  of  the  leaves.  Spray  with  nicotine  and  soap  (Formula 
27)  or  dust  thoroughly  with  5  per  cent  nicodust  as  soon  as  aphids 
appear. 

California  Peach  Borer. — See  "Peach." 

Cankerworms. — See  "General  Subjects." 

Cherry  Fruit  Sawfly,  Hoplocampa  cookei  Clarke. — The  small 
white  larvae  work  within  the  partly  developed  fruits  of  the  cherry 
and  plum  and  are  at  times  responsible  for  much  damage.  Their 
presence  is  indicated  by  the  dropping  of  fruit  and  by  the  small  round 
exit  holes  in  fruits  which  are  hardly  half -grown.  The  best  treatment 
is  the  application  of  arsenate  of  lead  (Formula  2)  just  when  the  petals 
are  opening. 

Cherry  Slug,  Caliroa  cerasi  (Linn.). — The  common  name  applies 
to  the  small  dark  green  or  blackish  sluglike  larvae  which  are  nearly 
one-half  inch  long  and  which  feed  upon  the  leaves  in  great  numbers 
almost  defoliating  the  trees  in  some  years.  Because  of  their  slimy 
covering  they  are  readily  killed  by  the  application  of  various  dusts, 
such  as  finely  ground  hydrated  lime,  ashes,  road  dusts,  etc.,  but  are 
best  controlled  by  the  applications  of  2  per  cent  or  5  per  cent  nicodust. 
The  regular  arsenate  of  lead  sprays  (Formula  2)  are  also  good. 

Pear  Thrips.— See  "Pear." 

Red  Humped  Caterpillar. — See  "Prune." 

Tent  Caterpillars. — See  "General  Subjects." 


16  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

CHRYSANTHEMUM 

Rust,  Puccima  chrysanthemi  Roze. — Small  dark  pustules  or  sori 
appear  on  the  lower  side  of  leaves.  Fertilize  and  irrigate  freely  to 
produce  vigorous  plants. 

Aphids  (Various  Species). — Spray  with  nicotine  and  soap  (Form- 
ula 27)  or  dust  with  5  per  cent  nicodust  when  the  insects  appear. 

Chrysanthemum  Gall  Fly,  Diarthronomyia  hypogaea  (Low). — The 
small  yellowish  or  white  larvae  cause  numerous  pointed  galls  on  the 
leaves  and  stems  and  seriously  injure  the  terminal  buds.  Great  num- 
bers of  minute  slender  red  eggs  are  laid  on  the  plants  in  the  spring 
and  early  summer,  and  these  may  be  readily  killed  by  repeated  appli- 
cations of  nicotine  and  soap  (Formula  27).  Trim  the  plants  to  the 
ground  in  spring  to  eliminate  hold-over  forms. 

Chrysanthemum  Leaf  Miner,  Phytomyza  chrysanthemi  Kow. — 
The  injury  due  to  this  insect  consists  in  numerous  mines  on  the  upper 
side  of  the  leaves  just  under  the  epidermis.  These  are  made  by  the 
small  whitish  maggots,  which  are  easily  killed  within  their  burrows  by 
applying  one  part  of  40  per  cent  nicotine  sulfate  to  600  parts  of  water. 

CITRUS  FRUITS  (Grapefruit,  Lemon,  Orange) 

Blast,  Black  Pit,  Bacterium  citriputeale  C.  0.  Smith. — Blast  occurs 
only  in  very  moist  seasons  and  districts;  black  pit  occurs  with  blast 
and  also,  rarely,  in  less  moist  localities.  Blast  is  a  watery  deterioration 
of  leaves  and  petioles  extending  to  a  shield-shaped  area  in  the  twig 
about  the  base  of  the  leaf.  Leaves  die  and  dry  up  in  place,  the  twig 
lesions  turn  dark,  dry  up,  and  heal,  and  shed  off  in  two  or  three  years. 
Where  several  leaves  are  killed,  the  twig  may  be  much  weakened  or 
die.  Black  pit  consists  of  dark,  sunken  spots  in  the  rind  of  the  fruit. 
They  do  not  decay.  Grow  bushy,  compact  trees  and  avoid  severe 
pruning.  Protect  the  orchard  with  windbreaks  against  prevailing 
rain  storms.  For  northern  California  conditions,  spray  from  October 
to  December  with  Bordeaux  or  ammonia  copper  carbonate,  repeat  as 
soon  as  the  fruit  is  off  or  before  January  1  with  Bordeaux. 

Blue  Mold,  Green  Mold,  Penicillium  sps.— Rots  the  entire  fruit, 
starting  in  spots  and  becoming  a  powdery  blue  or  green,  and  gray. 
Avoid  even  minutest  injuries  in  picking  and  handling  fruit. 

Brown  Rot,  Pythiacystis  citrophthora  S.  &  S.,  Cottony  Rot,  Sclero- 
tinia  libertiana  Fcl. — The  first  produces  a  firm  rot  of  the  fruit  with  a 
characteristic  odor  and  slight  surface  mold.  The  second  produces  a 
rather  soft  rot  with  copious  white  mycelium  in  which  are  embedded 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  17 

black  bodies  (sclerotia)  often  larger  than  rice  grains.  When  the 
disease  is  prevalent  spray  the  lower  branches  and  the  ground  beneath 
with  Bordeaux  mixture  (Formula  9).  Do  not  allow  boxes  of  fruit  to 
stand  over  night  in  the  orchard.  Use  bluestone  in  the  wash  water 
(Formula  12),  maintaining  a  constant  strength  of  1%  pounds  to 
1000  gallons.  Grade  out  very  carefully  all  orchard  infected  fruits 
before  storing. 

Damping  Off,  Armillaria  Root  Rot. — See  "General  Subjects." 

Gummosis,  Phythiacistis  citrophthora  Smith  &  Smith. — Copious 
exudation  of  gum  on  the  lower  part  of  the  trunk.  The  bark  of  the 
affected  part  dies  and  the  diseased  area  may  continue  to  spread  until 
the  tree  is  girdled  and  killed.  Cut  out  all  affected  bark  as  soon  as  dis- 
covered and  treat  the  wounds  with  Bordeaux  paste  (Formula  10) .  Do 
not  allow  water  to  stand  about  the  base  of  trees.  In  planting  keep 
the  point  of  budding  well  above  ground  and  never  allow  the  soil  to 
pile  up  around  the  trunk.  For  heavy  soil,  use  trees  high-budded  on 
sour  orange  root. 

Mottled  Leaf. — Add  as  much  organic  matter  to  the  soil  as  possible 
in  the  form  of  green  manure  crops,  bean  straw,  and  manure.  See  that 
water  penetrates  to  the  subsoil  and  keeps  it  uniformly  moist.  See 
"General  Subjects." 

Scaly  Bark. — Bark  at  first  becomes  roughened  in  a  small  area; 
roughening  spreads  and  deepens,  finally  gumming  heavily,  encircling 
the  trunk  or  limb  and  causing  its  death.  In  small  early  cases  on  trunks 
cut  out  to  the  wood;  in  later  larger  cases  scrape  off  outer  layer  of 
affected  bark,  leaving  the  inner  bark.  Cover  the  wounds  with  Bor- 
deaux paste  (Formula  10)  or  other  suitable  fungicide.  Cut  off  badly 
affected  branches.  "Watch  all  trees  very  closely  in  groves  where  the 
disease  is  present  and  eradicate  new  cases  at  first  appearance.  Do 
not  use  Bordeaux  if  the  trees  are  soon  to  be  fumigated  as  cyanide  is 
said  to  render  the  Bordeaux  coating  injurious. 

Aphids  (Various  Species) .—Use  nicotine  and  soap  spray  (Formula 
27)  or  a  5  per  cent  nicodust. 

Armyworms  and  Cutworms.— See  "General  Subjects." 
Citrus  Red  Spider,  Tetranychus  citri  McGregor  and  the  Two- 
Spotted  Mite,  Tetranychus  telarius  Linn. — The  citrus  red  spider  is 
bright  cardinal  red,  while  the  two-spotted  mite  is  yellow,  pale  green 
or  reddish  and  often  with  two  or  six  dark  spots  on  the  dorsum.  Dust 
with  sulfur  or  spray  with  lime-sulfur  1-50  or  wettable  sulfur  (Form- 
ula 14),  or  commercial  sulfur  paste  10  pounds  to  100  gallons  of  water. 


18  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

Citrus  Thrips,  Scirtothrips  citri  (Moult.). — Small  pale  yellow  in- 
sects less  than  one-thirtieth  inch  long  working  in  blossoms  and  on 
leaves  and  fruit.  This  insect  is  most  satisfactorily  controlled  by  a 
2  per  cent  solution  of  commercial  lime-sulfur,  but  may  also  be  con- 
trolled by  using  the  Government  formula  for  pear  thrips  (Formula 
24)  or  by  applications  of  6  per  cent  nicodust.  A  combination  of  mis- 
cible  oil  and  lime-sulfur  is  recommended  by  some  for  killing  the  gray 
citrus  scale  (Coccus  citricola  Campb.)  and  the  citrus  thrips  at  the 
same  time. 

Fuller's  Rose  Beetle,  Pantomorus  fulleri  (Horn). — A  small  gray 
snout  beetle  three-eighths  inch  long  which  attacks  young  buds  and 
foliage  of  citrus  trees.  The  adults  cannot  fly  and  may  be  kept  off  the 
trees  by  cotton  or  tanglefoot  bands  around  the  trunks. 

Mealybugs  (Various  Species  of  Pseudococcus) . — These  small,  flat, 
oval  insects,  covered  with  white  mealy  material,  are  well  known  to  most 
citrus  growers.  They  are  difficult  to  control,  but  may  be  most  satis- 
factorily handled  by  liberal  applications  of  carbolic  acid  emulsions 
(Formulas  26  and  26a)  and  by  miscible  oils.  Washing  with  water 
under  heavy  pressure  has  proved  satisfactory  under  certain  conditions. 
For  the  citrus  mealy  bug,  parasites  are  used  with  splendid  results 
along  the  coast.  The  control  of  ants  is  necessary  to  secure  beneficial 
results  from  natural  enemies  (see  ' '  Ants") . 

Scale  Insects  (Many  Species) — Fumigation  with  hydrocyanic  acid 
gas  is  best,  although  some  orchardists  secure  good  results,  particularly 
for  soft  brown  and  gray  citrus  scales,  by  repeated  and  thorough  appli- 
cations of  various  strengths  of  distillate  emulsions  (Formulas  20  and 
23)  and  miscible  oils. 

CORN 

Boil  Smut  or  Common  Smut,  Ustilago  zeae  (Beckm.)  Ung.— Tender 
tissues  of  tassel,  ear,  or  stalk  swell  into  large  soft  masses,  which  dry 
out,  becoming  fragile  and  filled  with  black  dust.  Sometimes  gather- 
ing up  and  destroying  the  smutted  stalks  before  the  smut  balls  dry 
is  recommended.  Seed  treatment  is  not  effective.  Often  serious  in 
California.  Rotation  is  perhaps  useful.  Diseased  corn  trash  and 
manure  are  infectious. 

Ear  Mold,  Diplodia  zeae  (Schw.)  Lev.  and  Fusarium  sp. — The  ears 
mold  in  the  field,  the  kernels  becoming  crusted  together  and  light. 
Sometimes  bad  in  late  corn  in  shallow  soil.  Use  early  varieties.  Har- 
vest and  cure  as  early  as  possible.    Avoid  over-irrigation. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  19 

Head  Smut,  Sphacelotheca  reiliana  (Kuehn.)  Clint. — Ear  and 
whole  top  of  plant  are  affected.    No  grain  formed.    See  "Sorghum." 

Angoumoise  Grain  Moth. — See  "Grain." 

Armyworms  and  Cutworms. — See  "General  Subjects." 

Corn  Earworm,  Chloridea  obsoleta  (Fab.). — The  larvae  are  nearly 
two  inches  long  when  full  grown  and  vary  in  color  from  yellowish  to 
brownish,  with  longitudinal  gray  and  white  stripes  and  with  eight 
small  dark  tubercles  on  each  segment.  They  work  chiefly  on  the  corn 
in  the  ear,  but  may  also  attack  the  tassels  and  leaves.  Clean  up  and 
burn  refuse  in  the  field.  Plow  in  fall  or  early  spring  to  expose  and 
kill  the  pupae.  Repeated  dusting  of  ears  with  powdered  arsenate  of 
lead  one  part  to  four  parts  of  hydrated  lime  gives  some  relief. 

Granary  and  Rice  Weevils. — See  ' '  Grain. ' ' 
Grasshoppers. — See  "General  Subjects." 
Wireworms. — See  "General  Subjects." 

COTTON 

Bean  Thrips. — See  "Bean."  This  insect  usually  appears  on  the 
cotton  late  in  the  season,  when  the  injury  is  not  of  sufficient  importance 
to  justify  control.    Early  infestations  should  be  promptly  dealt  with. 

Corn  Earworm. — See  "Corn."  Attacks  the  cotton  bolls.  Sweet 
corn  is  sometimes  planted  as  a  catch  crop.  Dusting  with  powdered 
arsenate  of  lead  or  calcium  arsenate  gives  good  results. 

Cotton  Leaf  Perforator,  Bucculatrix  thurberiella  Busck. — The 
larvae  are  pale  or  dark  greenish  and  less  than  one-half  inch  long. 
When  disturbed  they  wriggle  violently.  The  work  consists  in  per- 
forating the  leaves  with  very  many  holes  so  as  to  almost  entirely 
consume  them.  The  larvae  pupate  in  small,  white  ribbed  cocoons 
attached  to  the  leaves  or  stems  of  the  plants.  The  adults  are  white 
with  black  dots  and  other  black  markings. 

This  insect  normally  feeds  upon  wild  cotton,  but  in  recent  years 
has  invaded  the  cotton  belt  of  the  Southwest,  and  while  it  prefers  weak 
plants,  it  will  attack  perfectly  healthy  ones  as  well. 

Parasites  do  much  to  keep  the  insect  in  check  but  where  severe 
infestations  occur  dust  plants  with  calcium  arsenate  alone  or  with  lead 
arsenate,  one  part  to  four  parts  of  hydrated  lime.  From  20  to  30 
pounds  are  sufficient  for  an  acre  of  cotton. 

Red  Spider  or  Two-Spotted  Mite,  Tetranychus  telarius  Linn. — See 
"Bean," 


20  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

CUCUMBER 

Mildew,  Erysiphe  dehor earum  D.  C.  =  Oidium. — Fine  white  my- 
celium covers  the  leaves.  Dust  with  sulfur  at  first  appearance  or  with 
sulfur  nicodust  if  the  melon  aphis  is  also  present. 

Flea  Beetles  (Various  Species). — Small  flea-like  beetles  which  jump 
quickly  and  eat  small  holes  in  the  leaves.  Bordeaux  mixture  (Form- 
ula 9)  as  a  repellent  is  the  best  control  measure.  This  treatment  is 
also  recommended  for  mildew. 

Garden  Nematode. — See  ' '  General  Subjects. ' ' 

Melon  Aphis.— See  " Melon." 

Red  Spider  or  Two-Spotted  Mite.— See  "Bean." 

Western  Twelve-Spotted  and  Striped  Cucumber  Beetles,  Diabro- 
tica  soror  Lee.  and  D.  trivittata  Mann. — The  former  is  a  small  green 
beetle  with  twelve  black  spots  on  the  back  and  is  often  mistaken  for  a 
ladybird;  the  latter  is  a  brown  beetle  with  three  black  lines  on  the 
dorsum.  The  white  larvae  feed  upon  the  roots  and  may  be  controlled 
by  pouring  on  the  roots  a  cup  of  40  per  cent  nicotine  sulfate  diluted 
1  to  1000  parts  of  water.  Bordeaux  mixture  (Formula  9)  is  of  con- 
siderable value  as  a  repellent.  Arsenate  of  lead  (Formula  2)  may  also 
be  used  with  good  effect. 

CURRANT,  GOOSEBERRY 

Mildew,  Sphaerotheca  mors-uvae  (Schw.)  B.  &  C. — A  fine  white 
mycelium  grows  over  the  young  leaves  and  shoots  and  checks  their 
development.  Serious  on  some  varieties.  The  best  treatment  is  to 
spray  with  lime-sulfur  1-33  when  buds  commence  to  open  and  two  or 
three  times  thereafter  at  intervals  of  10  to  14  days.  "Where  serious 
cut  and  burn  diseased  tips  of  canes  while  dormant,  as  the  fungus  win- 
ters in  them  (from  U.  S.  D.  A.  Farmers'  Bull.  1024).  In  California, 
where  resistant  varieties  are  used,  a  dormant  spray  of  lime-sulfur  1-10, 
followed  by  dusting  with  sulfur  when  the  disease  first  appears,  has 
generally  been  effective. 

Currant  or  Gooseberry  Fruit  Fly,  Epochra  canadensis  Loew. — 
Small  white  maggots  in  the  fruit  at  picking  time.  Cultivate  thoroughly 
during  the  fall,  winter,  and  spring  months  to  expose  and  destroy  the 
hibernating  pupae. 

Flat-Headed  Apple  Tree  Borer.— See  " Apple." 

Imported  Currant  Borer,  Aegeria  tipuliformis  Clerck. — White 
caterpillars  nearly  one  inch  long  working  down  the  middle  of  the  stalks 
and  into  the  roots  of  the  plants.  Cut  out  and  burn  all  dead  and  in- 
fested canes  during  winter  and  remove  the  borers. 


ClRCLLAR  227]  PLANT  DISEASE  AND  PEST  CONTROL  21 

Red  Spider  or  Two-Spotted  Mite,  Tetranychus  telarius  Linn. — See 
"Bean."  Dust  with  sulfur  or  spray  with  wettable  sulfur  (Formula 
14)  or  sulfur  paste  (Formula  13). 

San  Jose  Scale. — See  "Apple." 

Combined  Sprays 
The  sulfur  sprays  will  control  both  the  mildew  and  the  red  spider. 

DAHLIA 
Mildew,  Erysiphe  sp. — White  spots  spread  over  lower  leaves.    Not 
serious.    Dust  with  sulfur. 
Bean  Aphis. — See  "Bean." 
Western  Twelve-Spotted  Cucumber  Beetle. — See  "Cucumber." 

DATE 

Date  Palm  Scale,  Parlatoria  Uanchardii  (Targ.). — A  small  gray 
and  white  scale,  less  than  one-sixteenth  inch  long,  often  occurring  in 
great  numbers  on  the  leaves.  It  may  be  controlled  by  cutting  away 
and  destroying  all  the  leaves,  burning  over  the  trunk  with  a  gasoline 
torch.  Offshoots  are  cleaned  up  by  heavy  fumigations  with  hydro- 
cyanic acid  gas.  This  insect  is  quarantined  by  the  Federal  Horticul- 
tural Board,  and  young  plants  may  be  obtained  only  from  uninfested 
territory. 

Dried  Fruit  Beetle.— See  "Prune." 

Indian  Meal  Moth. — See  "Prune."  This  insect  is  a  serious  pest 
of  dried  dates,  of  which  small  amounts  are  preferably  put  up  only  in 
insect-proof  containers  to  prevent  infestation. 

Marlatt  Scale,  Phoenicacoccus  marlatti  Ckll. — A  red-bodied,  cot- 
tony covered  scale,  considerably  larger  than  the  Date  Palm  Scale.  It 
is  chiefly  found  in  the  unfolding  leaves,  often  so  protected  as  to  be 
almost  impossible  of  control.  Fumigating  and  burning  over  the  trunks 
and  treating  liberally  with  carbolic  acid  and  oil  emulsions  give  some 
control,  but  eradication  on  a  tree  once  thoroughly  infested  is  appar- 
ently impossible.  This  pest  is  also  under  federal  quarantine,  and  new 
plants  may  be  obtained  only  from  uninfested  territory. 

Red  Spider.— See  "Citrus." 


22  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

FIG 

Smut,  Sterigmatocystis  ficum  (Reich.)  Hen. — The  inside  of  the  fig 

becomes  a  powdery,  purple  mass.    No  remedy  known. 

Souring  and  Splitting. — Due  to  unfavorable  atmospheric  and  soil 
moisture  conditions.  Choose  suitable  localities  and  regulate  the  soil 
moisture  with  greatest  care. 

At  least  two  canker  diseases  are  known  in  California,  and  twig 
blight  is  caused  to  a  limited  extent  by  Sclerotinia  libertiana  and 
Botrytis  cinerea.    None  of  these  appears  to  be  serious. 

Branch  and  Twig  Borer. — See  "Apricot." 

Mediterranean  Fig  Scale,  Lepidosaphes  ftcus  (Sign.). — Scales  re- 
semble small  oysters  and  infest  the  limbs,  twigs,  leaves,  and  fruit. 
Spray  with  distillate  emulsion  (Formula  23),  miscible  oil  or  crude 
oil  emulsion  (Formula  18)  during  the  winter  when  the  trees  are 
dormant. 

Nematodes. — Becoming  increasingly  serious.  No  remedy  known. 
See  "General  Subjects." 

Pomace  or  Vinegar  Fly,  Drosophila  melanogaster  Meigen. — Small, 
slender,  whitish  maggots  and  brown  or  orange-colored  flies  one-tenth 
inch  long,  often  occurring  in  great  numbers  in  figs  on  the  trees  and 
on  the  drying  trays.  Attacks  only  soured  fruit,  but  is  neither  respons- 
ible for  the  souring  nor  injurious  to  sound  fruit. 

GRAIN  (Barley,  Oats,  Wheat) 

Rustj  Puccinia  sps. — Pustules  of  pinhead  size,  round  or  elongated, 
break  through  the  surface  of  leaves  and  stems ;  mostly  reddish  at  first 
and  dusty,  later  black.  Serious  in  heavy  grain  in  moist  situations  or 
seasons.    No  remedy  known  but  resistant  varieties  may  be  used. 

Smut,  Ustilago  sps.  and  Tilletia  sps. — Mature  grain  has  black  con- 
tent and  gives  off  characteristic  odor.  Seed  of  wheat,  barley,  oats, 
Sudan,  millet  and  sorghum  should  be  carefully  cleaned  of  smut  balls, 
weed  seeds,  and  small,  cracked,  and  inferior  grains  before  treating. 
The  smut  balls  in  wheat  and  smut  masses  in  barley  may  be  cleaned  out 
in  fanning  mills  or  floated  out  in  water  and  skimmed  off.  Place  the 
cleaned  seed  in  half -filled  sacks  tied  at  the  end.  Immerse  these  sacks 
for  three  or  four  minutes  in  a  bluestone  solution  made  by  dissolving  1 
pound  of  bluestone  in  5  gallons  of  water  (Formula  11).  Drain  the 
sacks  until  dripping  no  longer  occurs,  then  dip  them  for  three  minutes 
in  a  milk  of  lime  made  by  slaking  1  pound  of  quicklime  in  10  gallons  of 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  23 

water.  The  lime  prevents  injury  to  the  germ  from  bluestone.  If  quick- 
lime cannot  be  secured,  air-slaked  lime,  1  pound  to  8  gallons  of  water 
may  be  used.  After  this  treatment  the  grain  should  be  spread  out  to 
dry,  after  which  it  may  be  planted  or  stored. 

Oats  are  especially  sensitive  to  bluestone,  and  for  them  it  is  better 
to  use  a  solution  of  formaldehyde,  1  pound  to  40  gallons  of  water,  for 
ten  minutes.  After  this  no  lime  dip  is  needed.  Barley  is  more  sensi- 
tive than  wheat  and  should  always  be  lime-dipped  after  treatment  with 
bluestone. 

Seed  scratched  or  injured  in  threshing  should  be  limed  after  dip- 
ping in  bluestone  solutions.  Scoured  seeds  should  not  be  dipped  in 
any  fungicidal  solution. 

Seed  wheat  and  barley  to  be  sown  in  dry  ground  or  to  be  stored 
longer  than  48  hours  must  not  be  treated  with  formaldehdye,  as  severe 
injury  may  follow. 

If  foggy  or  rainy  weather  is  liable  to  interfere  with  the  proper 
drying  of  lime-treated  seed,  heating  injury  may  be  avoided  by  soaking 
the  seed  for  10  or  15  minutes  in  water  before  dipping  in  the  bluestone 
solution.    The  lime  dip  may  then  be  omitted. 

Loose  smuts  of  wheat  and  sorghum  cannot  be  controlled  by  the 
above  treatment.  Loose  smuts  of  oats  and  barley  are  destroyed  by 
formaldehyde  solution  (1  pint  to  30  gallons  of  water)  soaking  for  10 
minutes.  Kernel  smut  of  sorghums  and  Sudan  grass  is  controlled  by 
soaking  the  seed  in  formaldehyde  solution,  as  above,  for  30  minutes  for 
grain  sorghums  and  60  to  90  minutes  for  sweet  sorghums  and  Sudan- 
Ergot  of  rye  and  rye  grass  is  controlled  by  floating  off  the  ergots  in  a 
strong  brine  solution  (40  pounds  salt  in  25  gallons  water)  and  rinsing 
with  clear  water,  or  by  holding  the  seed  for  a  year  before  sowing. 
Copper  carbonate  dust  intimately  mixed  with  wheat  seed  at  the  rate 
of  2  ounces  per  bushel  is  a  new  and  promising  fungicide  for  control 
of  bunt. 

Angoumoise  Grain  Moth,  Sitotroga  cerealella  Oliv. — A  small  tawny 
moth  found  in  granaries.  The  pale  yellow  caterpillars  feed  within 
the  kernels  of  stored  grain  and  corn,  escaping  through  a  round  hole. 
Control  measures  are  the  same  as  for  the  granary  and  rice  weevils 
(see  below). 

Aphids  (Many  Species). — Aphids  often  seriously  attack  grain. 
Control  methods  are  usually  too  costly  to  be  practicable.  Cutting  is 
often  resorted  to  in  order  to  save  that  part  of  the  crop. 

Armyworms  and  Cutworms. — See  "General  Subjects." 


24  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Granary  Weevil,  Calandra  granaria  Linn.,  and  Rice  Weevil,  C. 

oryzae  Linn. — Small  brown  weevils  not  over  one-sixth  inch  in  length, 
attacking  the  grain  in  storage.  Fumigate  with  carbon  bisulfide,  10 
to  30  pounds  to  1000  cubic  feet  of  air  space,  according  to  the  tightness 
of  the  container.  The  temperature  must  be  at  least  70°  F.  for  satis- 
factory results.  Hydrocyanic  acid  gas  may  also  be  used  as  a  fumigant, 
in  which  case  from  1  to  4  ounces  of  pure  sodium  cyanide  to  100  cubic 
feet  of  air  space  should  be  used.  Heating  the  grain  to  125°  F.  for 
several  hours  will  kill  all  the  weevils.  Keeping  the  grain  dry  and  well 
ventilated  will  largely  prevent  weevil  attack  in  storage. 

Grasshoppers. — See  ''General  Subjects." 

GRAPE,  RAISIN 

Crown  Gall  =  Black  Knot,  Bacterium  tumefaciens  S.  &  T. — May 
be  treated  with  some  success.  Not  usually  very  injurious.  See  ' '  Gen- 
eral Subjects." 

Little  Leaf,  Apoplexy,  Obscure  Diseases. — See  "Physiological 
Diseases"  under  "General  Subjects." 

Mildew,  Uncinula  spiralis  B.  &  C=U.  necator  (Schw.)  Burr. — 
White  mycelium  spreads  over  young  leaves,  canes,  and  fruits,  checking 
growth ;  the  leaves  are  deformed  and  may  drop ;  the  surface  of  the 
fruit  hardens  and  darkens  and  the  fruit  often  cracks,  or  may  drop. 
Dust  with  sulfur  when  the  shoots  are  about  6  inches  long  and  again 
just  before  the  blossoms  open,  being  careful  not  to  miss  a  single  leaf. 
If  the  vines  were  affected  the  previous  year  do  not  wait  until  the 
mildew  appears.  In  cool  or  moist  locations  a  third  sulfuring  when 
the  grapes  are  as  large  as  peas  and  a  fourth  when  they  are  two-thirds 
grown  may  be  necessary.  In  these  later  treatments  the  sulfur  should 
be  dusted  only  on  the  fruit  and  the  centers  of  the  vines.  If  the  larvae 
of  leaf-hoppers  are  present  use  nico-sulfur  instead  of  sulfur. 

Achemon  Sphinx  Moth,  Pholus  achemon  (Drury). — Large  green 
and  pinkish  caterpillars  with  oblique  whitish  bars  on  the  sides.  Often 
abundant  and  doing  great  damage  by  stripping  the  vines.  Adult 
moths  dull  gray  with  brown  marks  and  pink  hind  wings.  Spray  vines 
with  arsenate  of  lead  (Formula  2),  to  which  is  added  1  pint  of  40 
per  cent  nicotine  sulfate  to  every  200  gallons,  or  dust  with  powdered 
arsenate  of  lead,  1  part  to  4  parts  of  hydrated  lime  or  flowers  of  sulfur. 

Armyworms  and  Cutworms. — See  "General  Subjects." 


Circular  227]  plant  DISEASE  AND  PEST  CONTROL  25 

California  Grape  Root  Worm,  Bromms  obscurus  (Linn.). — The 
adult  beetles  are  black  or  brown  and  three-sixteenths  inch  long.  They 
eat  long  slender  holes  in  the  leaves.  The  small  white  grubs  feed  on 
the  roots  of  the  vines.  Cultivate  thoroughly  close  to  the  vines  during 
the  winter  to  kill  hibernating  larvae.  As  soon  as  beetles  appear  in 
the  spring  spray  with  arsenate  of  lead,  6  pounds  of  paste  or  3  pounds 
of  powder  to  100  gallons  of  water,  or  dust  with  one  part  of  powdered 
arsenate  of  lead  to  four  parts  of  hydrated  lime  or  sulfur. 

Dried  Fruit  Beetle. — On  raisins,  see  "Prune." 

Grape  Leaf -hopper,  Erythroneura  comes  (Say). — The  immature 
forms  or  nymphs  are  white  or  pale  yellow,  while  the  adults  are  pale 
yellow  with  numerous  small  reddish  marks  all  over  the  dorsum.  All 
forms  feed  on  the  under  side  of  the  leaves,  causing  them  to  turn  yellow 
and  drop  prematurely.  Clear  weeds  and  refuse  from  around  the 
vineyards  and  practice  clean  culture  to  reduce  the  number  of  over- 
wintering adults.  Before  the  young  nymphs  develop  wings  spray 
thoroughly  with  nicotine  and  soap  (Formula  27),  or  with  the  follow- 
ing: 40  per  cent  nicotine  sulfate,  1  pound  ;  liquid  soap,  %  gallon  (hard 
soap,  2  pounds)  ;  water,  200  gallons.  The  young  and  adults  may  also 
be  killed  by  thoroughly  dusting  with  a  10  per  cent  nicodust,  or  a 
6  per  cent  nicosulfur  dust,  which  latter  will  also  control  mildew. 

Grape  Phylloxera,  Peritymbia  vitifoliae  (Fitch). — The  presence 
of  the  phylloxera  is  indicated  by  weak  and  dying  vines,  and  usually 
occurs  in  spots.  The  insect  is  a  minute,  yellow  louse  which  feeds  upon 
the  roots.  To  disinfect  cuttings  or  rootings  before  planting,  dip  in 
hot  water  122°  F.  for  five  minutes.  For  permanently  resistant  vines, 
graft  European  varieties  on  certain  American  roots  (see  Circular  No. 
226,  Calif.  Agr.  Exp.  Sta.,  Univ.  of  Calif.,  Dec,  1920). 

Grasshoppers. — See  "General  Subjects." 

Indian  Meal  Moth. — On  raisins,  see  "Prune." 

Mealybug,  Pseudococcus  maritimus  Ehrh.  =  P.  bakeri  Essig. — 
Easily  distinguished  by  the  small  oval,  flat  bodies  covered  with  white 
cotton-like  wax  and  by  the  cottony  egg  masses  among  the  bunches  of 
grapes.  Difficult  of  control,  but  best  results  have  been  obtained  by 
burning  sulfur  under  a  tent  over  the  vines.  (See  Monthly  Bull.,  Cal. 
State  Dept.  Agr.,  Sacramento,  Vol.  IX,  p.  26,  1920.    Also  see  "Pear.") 

HOLLYHOCK 

Rust,  Puccinia  malvacearum  Mont. — Prominent  red  sori  or  pus- 
tules push  out  on  the  lower  surface  of  the  leaves  and  on  petioles  and 
stems,  often  causing  distortion.  Fertilize  and  water  freely  to  promote 
vigorous  growth. 


26  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  Painted  Lady  Butterfly,  Vanessa  caryae  Hubn. — The  yellowish 
or  black  spiny  caterpillars,  which  are  about  one  inch  long,  feed  upon 
the  leaves,  which  they  draw  together  with  webs  for  protection.  Con- 
trol is  best  accomplished  by  using  40  per  cent  nicotine  sulfate,  1  part 
to  600  parts  of  water,  and  spraying  the  plants  thoroughly. 

HOP 

Hop  Aphis,  Phorodon  humuU  (Schr.). — A  pale  green  aphid  at- 
tacking the  young  shoots  and  leaves.  Dust  thoroughly  and  as  often 
as  necessary  with  5  per  cent  nicodust  or  spray  until  injury  ceases  with 
nicotine  and  soap  (Formula  27). 

Hop  Flea  Beetle,  Psylliodes  punctulata  Mels. — A  small  green  or 
bronze  metallic  beetle,  one-tenth  inch  long,  attacking  the  foliage. 
Jumps  quickly  when  disturbed.  The  most  efficient  method  of  control 
consists  in  putting  tanglefoot  bands  around  the  bases  of  the  vines  and 
around  the  poles.  These  not  only  prevent  the  beetles  from  climbing 
the  vines  but  catch  great  numbers  of  them. 

Red  Spider  or  Two-Spotted  Mite.— See  "Bean." 

LOQUAT 

Pear  Blight,  Bacillus  amylovorus  (Burr.)  Detoni. — Limb  and  body 
blight  is  sometimes  very  severe.    See  ' '  Pear. ' ' 

Scab,  Fusicaladium  eryobotryae  Sciala. — Eesembles  scab  of  pear 
and  apple,  but  is  more  injurious  to  expanding  foliage.     See  "Pear." 

Green  Apple  Aphis. — See  "Apple." 

San  Jose  Scale. — See  "Apple." 

MELON  (Casaba,  Cantaloupe,  Pumpkin,  Squash,  Watermelon) 

Wilt,  Fusarium  sp. — Well  grown  watermelon  plants  wilt  and  die, 
leaving  the  field  nearly  bare.  Plant  on  fresh  soil.  Melons  cannot  be 
grown  for  several  years  on  infected  ground.  Other  melons  are  not 
often,  if  ever,  affected  in  California. 

Flea  Beetles. — See  "Cucumber." 

Melon  Aphis,  Aphis  gossypii  Glover. — A  small,  dark  green  louse 
occurring  in  great  numbers  on  the  plants  and  doing  great  damage. 
Destroy  first  infested  plants  as  soon  as  discovered  in  spring,  or  spray 
with  nicotine  sulphate,  40  per  cent,  1  part  to  1000  parts  of  water.  A 
5  per  cent  nicodust  also  gives  very  good  results  and  is  much  more 
easily  and  quickly  applied. 

Nematode. — See  "General  Subjects." 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  27 

Squash  Bug,  Anasa  tristis  De  Geer. — The  young  hugs  are  gray 
with  black  antennae,  legs,  and  thorax,  the  adults  of  a  uniform  dull 
grayish-brown  above,  mottled  yellowish  beneath,  and  about  three- 
quarters  inch  long.  Control  measures  should  be  directed  against  the 
immature  forms,  and  consist  in  the  use  of  one  part  of  40  per  cent 
nicotine  sulfate  to  600  parts  of  water.  A  10  per  cent  nicodust  kills 
many.  Hand  picking  the  adults  in  the  spring  is  successful  in  small 
gardens. 

Western  Twelve-Spotted  and  Striped  Cucumber  Beetles.— See 
' '  Cucumber. ' ' 

NURSERY  STOCK 

Failure  to  Grow  After  Planting  in  Orchard. — Very  rarely  due  to 
specific  disease.  Usually  caused  by  freezing,  drying,  or  water  soaking 
of  trees  before  or  after  planting ;  planting  too  deep ;  cold,  wet,  or  hot 
weather  after  planting ;  or  some  other  condition  unfavorable  to  growth. 
Buy  from  the  nearest  reputable  nursery.  Pay  for  good  trees  and  see 
that  they  are  handled  and  planted  carefully.  Replant  all  that  do  not 
grow  well  the  first  season. 

Lemon  Brown  Rot  or  Pythiacistis,  Pythiacistis  citropJithora  S.  & 
S. — Dead  spots  up  to  several  inches  long  develop  on  the  trunk,  mostly 
above  the  bud  union.  Caused  by  soil  infection  in  very  wet  conditions. 
Spray  trees  with  Bordeaux  mixture  before  digging  and  after  healing 
in.  Soil  for  healing  in  should  be  well  drained  or  under  cover.  Active 
only  in  very  wet  seasons. 

Nematode,  Crown  Gall. — Very  carefully  avoid  planting  affected 
trees.  If  a  large  percentage  of  a  plot  of  trees  is  affected,  those  appar- 
ently healthy  are  of  doubtful  value.     See  "General  Subjects." 

Citrus  Trees. — For  scale  insects,  defoliate  and  fumigate  with  hydro- 
cyanic acid  gas.    Rejecting  infested  stock  is  the  only  safe  procedure. 

Deciduous  Trees. — For  borers  and  other  insects,  fumigate  with 
hydrocyanic  acid  gas.  Rejecting  infested  stock  is  the  only  safe  pro- 
cedure. '   ■  '  •'   ' 

OAT.     See  Grain 

OLIVE 

Peacock  Spot,  Cycloconium  oleaginum  Cast. — Blackish  round  spots, 
one-eighth  to  one-quarter  inch  in  diameter,  on  the  surface  of  green 
leaves  but  not  killing  the  darkened  area.  Is  apparently  of  very  slight 
importance  in  California. 

Armillaria,  Wood  Decay.— See  "General  Subjects." 


28  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Die-back  ===  Exanthema. — Bushy  phase  characterized  by  repeated 
death  of  terminal  buds  and  branching  out  below ;  leaves  show  deform- 
ities. In  die-back  phase  there  is  usually  dropsy-like  puffing  of  bark 
on  branches  and  limbs  and  unusual  prominence  of  lenticels  in  the 
smooth  bark,  with  dying  back.  Secure  uniform  moisture  and  good 
drainage.  Add  organic  material  to  soil  by  green  manure  crops,  mulch, 
or  manure.  Replace  olives  with  plums,  peaches,  or  other  crop  where 
die-back  is  very  bad.  See  "Physiological  Diseases,"  under  "General 
Subjects. ' ' 

Dry  Rot,  Bitter  Pit. — Dry  spots  appear  in  the  flesh  of  the  fruit. 
See  "Physiological  Diseases,"  under  "General  Subjects."  No  effec- 
tive treatment  known  except  good  general  care. 

Olive  Knot  =  Tuberculosis,  Bacterium  savastanoi  E.  F.  Smith  = 
Pseudomonas  oleae. — Rounded  rough  swellings,  from  very  small  up 
to  several  inches  in  diameter,  appear  on  twigs,  limbs,  trunk,  or  roots, 
mostly  at  leaf  scars  or  wounds,  also  rarely  on  fruit  pedicles  and  leaves. 
Cut  out  thoroughly  at  first  appearance  and  disinfect.  See  "Pear 
Blight"  and  "Crown  Gall."  The  Mission  is  more  resistant  than  the 
Manzanillo  or  some  oil  varieties. 

Black  Scale,  Saissetia  oleae  (Bern.). — See  "Apricot."  Attacking 
chiefly  the  twigs.  Spray  with  distillate  emulsion  (Formula  23)  or 
miscible  oil,  December  to  February. 

Branch  and  Twig  Borer,  Polycaon  confertus  Lee. — See  "Apricot." 
This  is  often  a  serious  pest  of  young  olive  trees. 

Ivy  or  Oleander  Scale,  Aspidiotus  hederae  Vail. — A  small  circular, 
flat,  gray  scale  occurring  on  the  leaves  and  fruit,  sometimes  causing 
discolored  spots  on  the  ripening  olives.    Control  as  for  black  scale. 

Olive  Bark  Beetle,  Leperisinus  californicus  Swaine. — The  small 
white  larvae  work  in  the  cambium  layer  just  under  the  bark  and  the 
adults  bore  small,  round  exit  and  entrance  holes  through  the  bark. 
Occurs  in  the  southern  part  of  the  state.  Burn  prunings  and  remove 
all  dead  and  infested  portions  of  the  trees. 

ONION 

Downy  Mildew,  Peronospora  schleideni  Ung. — Areas  on  leaves  or 
stems  show  a  violet  tinted  fuzz.  These  areas  rapidly  fade  and  collapse 
if  the  weather  is  moist,  and  the  disease  may  spread  rapidly.  Not  suc- 
cessfully controlled  in  wet  seasons.  Bordeaux  mixture  found  useful 
in  some  cases ;  it  should  be  used  with  resin  fish-oil  soap  or  other 
spreader.     See  "Spreaders,"  pp.  68-69,  also  "Asparagus." 

Armyworms  and  Cutworms. — See  "General  Subjects." 


ClECULAR   227]  PLANT  DISEASE  AND  PEST  CONTROL  29 

Onion  Maggot,  Hylemyia  antiqua  Meig. — Small,  white  maggots 
attacking  the  onions  beneath  the  ground.  Practice  clean  culture  and 
destroy  all  refuse  onions  in  the  fall.  Plow  and  cultivate  thoroughly 
during  winter  and  spring.  Considerable  protection  is  gained  by  spray- 
ing the  plants  repeatedly  with  carbolic  acid  emulsion  (Formula  26, 
diluting  stock  solution  1  to  40). 

Onion  Thrips,  Thrips  tabaci  Lind. — Minute,  slender,  pale  yellow 
insects  occurring  in  great  numbers  on  the  leaves,  causing  them  to  turn 
gray  and  wither.  Spray  with  1  part  of  40  per  cent  nicotine  sulfate 
to  200  parts  of  water  or  apply  5  per  cent  nicodust. 

Wireworms. — See  "General  Subjects." 

PEA 

Bacterial  Blight  or  Bacteriosis,  Pseudomonas  pisi  Sack. — Exten- 
sive, watery,  olive-green  blisters  appear  on  stems  and  leaves  in  wet 
weather  following  cold.  Many  affected  areas  dry  up,  others  kill  the 
stem.  In  some  wet  situations  practically  every  plant  has  been  killed. 
Control  probably  the  same  as  for  blight. 

Blight,  Mycosphaerella  pinocles  Berk.  &  Blox  =  Ascochyta. — 
Sunken  dead  spots  form  on  pods,  leaves,  and  stems,  one-quarter  inch 
or  less  in  diameter;  center  of  spot  on  pod  becomes  gray  or  pinkish, 
with  a  dark  border ;  on  leaf  and  stem  spots  are  more  often  merely  dark. 
Young  stems  may  be  killed.  Experiments  indicate  spraying  is  imprac- 
tical. Keep  pea  crop  and  diseased  material  off  the  land  for  two  years. 
Seed  infection  rare  in  California.    Avoid  too  low,  wet  land. 

Mildew,  Erysiphe  polygoni  D.  C. — Powdery  white  growth  spreads 
over  the  foliage,  injurying  plants.  Troublesome  in  summer  or  when 
rains  are  light  or  lacking.  Dust  with  sulfur  on  first  appearance  or 
nicosulfur  dust  if  aphids  are  abundant,  and  repeat  if  necessary. 

Armyworms  and  Cutworms. — See  "General  Subjects." 
Pea  Aphis,  Macrosiphum  pisi  (Kalt.). — A  large  green  aphid  at- 
tacking the  terminal  shoots  and  leaves  of  the  vines.  It  is  difficult  of 
control  because  of  the  expense  involved,  but  can  be  killed  by  repeated 
applications  of  a  10  per  cent  nicodust  or  a  nicotine  spray  (Formula 
27a,)  or  a  6  per  cent  nicosulfur  dust  to  also  control  mildew. 

Pea  Weevil,  Bruchus  pisorum  Linn. — A  small  gray  and  white 
weevil  attacking  the  pea,  much  as  the  bean  weevil  attacks  the  bean, 
but  the  pea  weevil  infests  the  peas  in  the  field  and  the  adults  do  not 
emerge  until  the  following  spring.  Unlike  the  bean  weevil,  however, 
it  never  reinfests  stored  peas.  Treatment  is  the  same  as  for  bean 
weevil.    See  "Bean." 


30  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

PEACH 

Armillaria,  Wood  Decay,  Crown  Gall,  Nematode. — See  ' '  General 
Subjects." 

Blight,  Coryneum  beijerinckii  Oud.,  Curl  Leaf,  Exoascus  deformans 
Fcl. — In  blight;  buds  are  killed  during  winter,  sunken  round  spots  are 
killed  in  one-year  twigs,  and  in  spring  a  shot-hole  effect  appears  on 
leaves;  later  the  twig  spots  gum  profusely  and  gradually  heal  over 
unless  the  twig  is  killed.  In  curl  leaf,  young  leaves  and  sometimes 
shoot  tips  become  much  thickened  and  ruffled.  Later  they  become 
powdery,  fade  and  drop  early.  The  tree  is  weakened  through  loss  of 
foliage.  Spray  with  Bordeaux  (Formula  9)  or  lime-sulfur  1-10  be- 
tween November  15  and  December  15.  Repeat  with  lime-sulfur  as 
blossoms  begin  to  open.  Peaches  can  not  be  sprayed  after  leaves  ap- 
pear with  these  sprays  without  serious  injury. 

Brown  Rot,  Sclerotinia  cinerea  (Bon.)  Schrot. — Sometimes  im- 
portant in  causing  decay  of  late  ripening  fruit  in  moist  regions  near 
the  coast.  See  "Apricot."  Control  for  fruit  rot  not  developed  in 
California. 

Green  Rot. — See  "Apricot." 

Little  Leaf. — See  "Physiological  Diseases"  under  "General  Sub- 
jects." 

Powdery  Mildew,  Sphaerotheca  pannosa  var.  persicae  (Wallr.) 
Lev. — See  "Apple  Mildew."  Also  attacks  the  fruit.  Spray  with 
lime-sulfur  as  for  curl  leaf.  Prune  to  thin  foliage.  Dust  with  flowers 
of  sulfur  at  first  indication  of  mildew  and  repeat  as  necessary. 

Black  Peach  Aphis,  Aphis  persicae-niger  Smith. — A  shiny  black 
aphid  occurring  in  great  numbers  on  the  young  tender  shoots.  Spray 
with  nicotine  and  soap  (Formula  27)  or  dust  with  5  per  cent  nicodust 
as  soon  as  the  insects  appear. 

Black  Scale.— See  "Apricot." 

Branch  and  Twig  Borer,  Polycaon  confertus  Lee. — See  "Apricot." 

Brown  Apricot  Scale. — See  "Apricot." 

California  Peach  Borer,  Aegeria  opalescens Hy.  Edw. — White  cat- 
erpillars attaining  one  and  one-half  inches  in  length  which  burrow 
under  the  bark  at  the  base  of  the  trees,  often  extending  their  tunnels 
down  into  the  bases  of  the  main  roots.  Often  serious,  as  they  may 
completely  girdle  the  trees.  Dig  out  the  worms  carefully  in  the  fall 
and  spring  and  paint  over  the  wounds  with  a  good  asphaltum  paint. 

Cankerworms. — See  "General  Subjects." 

Flat-Headed  Apple  Tree  Borer.— See  "Apple." 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  31 

Peach  Rust  Mite,  Phyllocoptes  cornutus  Banks. — A  microscopic 
mite  causing  a  silvering  of  the  leaves.  Spray  in  winter  when  the  trees 
are  dormant  or  when  buds  swell  in  the  spring  with  lime-sulfur  1-lb 
to  kill  mites  hibernating  in  buds. 

Peach  Twig  Borer,  Anarsia  lineatella  Zeller. — A  small,  dark- 
reddish  caterpillar,  scarcely  one-half  inch  long,  which  burrows  into 
and  kills  the  young  tender  tips  of  the  twigs  and,  later  on,  may  infest 
the  fruit  to  some  degree.  The  minute  young  forms  hibernate  in  small 
cells  in  the  bark  and  are  effectively  killed  in  the  early  spring  of  the 
year  with  lime-sulfur  1-10  applied  just  as  the  blossom  buds  begin  to 
open,  which  is  before  the  larvae  are  able  to  enter  the  expanding  leaf 
buds. 

Red  Spider.— See  "Almond"  and  "Prune." 

San  Jose  Scale. — See  "Apple." 

Shot  Hole  Borer.— See  "Apricot." 

Tent  Caterpillars. — See  "General  Subjects." 

Wheat  Thrips,  Frankliniella  tritici  (Fitch). — This  minute  orange 
and  yellow  thrips  often  does  considerable  damage  to  the  young  fruit 
at  blossoming  time  and  later.  For  control  see  pear  thrips  under 
"Pear." 

Combined  Spraying 
Two  applications  of  lime-sulfur  as  recommended  above  will  control 
all  of  the  usual  diseases  and  pests  of  the  peach  in  California  which 
can  be  reached  by  any  spray  treatment,  but  lime-sulfur  has  occasion- 
ally been  reported  as  causing  injury  when  applied  in  the  bloom. 

PEAR 

Black  End. — Is  presumably  a  physiological  disease  comparable  to 
blossom  end  rot  of  tomatoes.  No  recommendation  as  yet  except  to 
give  good  care,  especially  as  to  drainage. 

Black  Leaf.— See  "Sour  Sap"  under  "General  Subjects." 
Blight,  Bacillus  amylovorits  (Burr.)  Detoni. — Tender  growth  be- 
comes watery,  darkens  rapidly,  wilts,  and  dies ;  usually  minute  beads 
of  viscid  material  exude ;  they  dry  in  the  same  form  and  show  a  solid 
mass  of  bacteria  when  moistened  in  water ;  in  heavier  bark  the  exudate 
may  be  more  copious,  or  lacking ;  the  diseased  tissue  may  be  recognized 
by  cutting  into  it.  Watery,  reddish  or  somewhat  dark  streaked  areas 
indicate  blight.  Any  succulent  part  of  the  top  may  be  attacked,  or 
the  root.  Cut  out  all  affected  parts  very  thoroughly.  Work  especially 
on  "hold-over"  in  large  limbs,  trunks,  and  roots  during  the  winter. 


32  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Disinfect  tools  and  cuts  freely.  A  new  system  is  being  largely  used 
in  which  only  the  outer  bark  is  cut  away,  leaving  the  cambium.  Keep 
close  watch  of  the  surface  to  check  new  development  of  infection. 
Mercuric  cyanide  and  corrosive  sublimate,  one  part  of  each  to  500  of 
water  (Formula  28a),  is  widely  used  for  disinfection.  Keep  all  suckers 
and  spurs  off  of  root  and  body.  In  new  plantings  in  blight  regions, 
top-work  on  resistant  varieties.  Surprise,  Ussuriensis,  and  others  are 
being  used  and  promise  well. 

Scab,  Venturia  pyrina  Aderh.  =  Fusicladium. — Dark  velvety 
mold  patches  appear  on  young  fruit  and  leaves;  badly  affected  fruit 
drops,  but  much  remains,  the  dark  areas  becoming  hard  and  rough 
and  often  cracked,  deforming  the  fruit.  Spray  with  lime-sulfur  1-12 
or  Bordeaux  (Formula  9)  just  as  the  cluster  buds  are  opening. 
Repeat  when  the  first  blossoms  are  open. 

Baker's  Mealybug,  Pseudococcus  maritimus  Ehrh.  =  P.  bakeri 
Essig. — Small,  oval,  flat  insect  less  than  one-quarter  inch  long  and 
covered  with  white  powdery  wax  and  normally  with  several  white,  tail- 
like filaments  nearly  half  as  long  as  the  body.  The  egg  sacs  look  like 
small  masses  of  cotton.  The  insects  occur  under  the  bark,  on  the  under 
side  of  limbs,  in  cracks,  wounds,  and  in  the  blossom  end  of  the  fruit. 
Control  measures  are  difficult  and  consist  of  repeated  applications  of 
crude  carbolic  acid  and  distillate  emulsion  (Formula  26a)  during  the 
winter  months  and  until  the  buds  begin  to  open  in  the  spring.  Scrape 
the  rough  bark  from  the  trunks  and  larger  limbs  so  as  to  expose  the 
mealybugs  to  the  spray.  If  the  fruit  is  infested,  spray  during  the 
summer  with  water  under  heavy  pressure  to  wash  the  bugs  away. 

Branch  and  Twig  Borer. — See  "Apricot." 

Brown  Apricot  and  Other  Soft  Scales. — See  "Apricot." 

Cankerworms. — See  "General  Subjects." 

Cherry  or  Pear  Slug. — See  ' '  Cherry. ' ' 

Codling  Moth. — See  "Apple."  The  control  of  this  insect  on  pears 
is  not  so  difficult  as  on  apples,  but  thorough  work  is  necessary  to  insure 
clean  fruit,  particularly  in  districts  where  large  acreages  of  pears  are 
grown. 

Fruit  Tree  Roller.— See  "Apple." 

Green  Apple  Aphis. — See  "Apple." 

Italian  Pear  Scale,  Epidiaspis  piricola  Del  G. — A  small  gray  cir- 
cular scale,  the  body  being  dark  red,  usually  occurring  under  the 
moss  or  old  bark;  but  it  may  cover  the  trunks  and  all  of  the  main 
branches  of  the  tree.     Causes  sunken  areas  in  old  limbs  and  greatly 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  33 

weakens  the  tree.  Spray  in  the  winter  months,  preferably  in  January 
and  February,  with  crude  oil  emulsion  (Formula  18),  distillate  sprays 
(Formulas  20  to  23),  or  miscible  oils.  The  crude  oil  emulsions  are 
preferable.  Thoroughly  drench  the  limbs  and  trunks.  (See  Cir.  No. 
224,  Calif.  Agr.  Exp.  Sta.,  Univ.  Calif.,  Dec,  1920.) 

Pear  Leaf  Blister  Mite,  Eriophyes  pyri  (Pagen.). — A  microscopic 
mite  causing  pinkish  and  yellowish  blisters  or  marks  on  the  young 
terminal  leaves  and  occasionally  reddish  blotches  on  the  young  fruit. 
Spray  in  November  or  February  with  lime-sulfur  1-10  to  kill  hiber- 
nating mites  in  buds. 

Pear  Root  Aphis,  Eriosoma  languinosa  (Hartig). — A  small  dark 
aphid  covered  with  white  cottony  material  and  greatly  resembling 
the  woolly  apple  aphis,  but  attacks  only  the  pear  roots.  For  control 
see  woolly  aphis  under  "Apple."  Eliminate  young  stunted  trees  and 
replant  healthy  ones.  The  Japanese  root  is  much  more  resistant  to 
this  pest  than  the  French. 

Pear  Thrips,  Taeniothrips  inconsequens  Uzel. — Small,  slender, 
black  insect  one-sixteenth  inch  long,  appearing  before  or  at  the  time 
the  blossom  buds  begin  to  open  and  continuing  until  after  blooming- 
season.  The  young  or  white  thrips  work  in  the  late  blossoms,  but 
chiefly  on  the  young  fruit  and  leaves.  Spray  as  often  as  necessary 
with  the  government  formula  (Formula  24)  or  dust  repeatedly  with 
5  per  cent  or  6  per  cent  nicodust.  Watch  for  adult  black  thrips  as 
soon  as  the  buds  begin  to  open  and  apply  control  measures  as  soon 
as  any  number  of  the  insects  appear.  (See  Cir.  No.  223,  Calif.  Agr. 
Exp.  Sta.,  Univ.  Calif.,  Nov.,  1920.) 

Red  Humped  Caterpillar. — See  "Prune." 

San  Jose  Scale. — See  "Apple."  Treatment  for  the  Italian  pear 
scale  above  will  also  suffice  for  this  insect. 

Combined  Spraying 

1.  For  scale  of  any  kind  and  for  moss  and  a  general  clean-up,  use 
a  winter  spray  of  lime-sulfur  1-10,  crude  oil  emulsion  (Formula  18), 
or  miscible  oil. 

2.  For  scab  and  thrips  use  Bordeaux  mixture  (Formula  9),  or 
lime-sulfur  1-10  as  cluster  buds  are  opening,  adding  an  extra  10  pounds 
of  lime  and  1  pound  of  40  per  cent  nicotine  sulfate  to  each  200  gallons 
of  spray.  Oil  sprays  should  not  be  mixed  with  lime-sulfur  or  Bordeaux 
mixture  for  this  purpose. 


34  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

3.  For  scab  and  thrips,  repeat  "2"  when  first  blossoms  are  about 
to  open. 

4.  For  codling  moth  and  late  scab  infection,  spray  when  petals  are 
falling  with  8  pounds  of  lead  arsenate  in  200  gallons  of  1-30  lime- 
sulfur  or  200  gallons  of  Bordeaux  mixture. 

PLUM,  PRUNE 

Armillaria,  Wood  Decay,  Crown  Gall,  Sour  Sap. — See  "General 
Subjects. ' ' 

Brown  Rot. — Not  often  serious.    See  "Apricot." 

Leaf  Spot,  Coryneum  b&ijerinckvi  Oud. — See  "Apricot,"  "Peach," 
and  "Almond." 

Black  Scale.— See  "Apricot." 

Brown  Apricot  Scale. — See  "Apricot." 

Branch  and  Twig  Borer  .—See  "Apricot." 

California  Peach  Borer. — See  "Peach." 

Cankerworms. — See  "General  Subjects." 

Cherry  Fruit  Sawfly. — See  "Cherry."  Also  attacks  varieties  of 
plums. 

Citrus  Red  Spider,  Tetranychus  citri  McGregor. — See  "Two- 
Spotted  Mite"  below. 

Dried  Fruit  Beetle,  Carpophilus  hemipterus  (Linn.). — A  small 
black  beetle  less  than  one-quarter  inch  long  with  a  reddish  spot  near 
the  middle  of  the  dorsum.  The  adults  and  small  yellowish  or  whitish 
larvae  feed  on  the  dried  fruit  and  continue  to  breed  indefinitely  in 
storage.  They  may  be  controlled  by  fumigation  as  recommended  for 
grain  weevil.    See  "Grain." 

Flat-Headed  Apple  Tree  Borer.— See  "Apple." 

Fruit  Tree  Leaf  Roller.— See  "Apple." 

Indian  Meal  Moth,  Plodia  inter punctella  Hiibn. — The  caterpillars 
are  white  or  pinkish  and  about  one  inch  long.  They  feed  on  the  dried 
fruit,  through  which  they  work  their  way  to  all  parts,  leaving  behind 
a  trail  of  excrement,  webbing,  and  spoiled  fruit.  Their  presence  is 
usually  first  indicated  by  webbing  on  the  fruit  or  around  the  sides  of 
the  container.  The  adults  are  small,  slender,  silvery  gray  moths  with 
the  apical  ends  of  the  wings  coppery.  This  insect  is  controlled  in  the 
same  way  as  the  granary  weevil  (see  "Grain").  Dipping  the  fruit 
in  scalding  water  prior  to  packing  kills  all  forms  of  this  insect.  Small 
packages  of  dried  fruit  should  be  made  insect  proof  to  prevent  infest- 
ation in  warehouses  and  storerooms. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  35 

Italian  Pear  Scale. — See  "Pear." 

Mealy  Plum  Louse,  Hyalopterus  arundinis  (Fabr.). — A  pale  green 
aphid  covered  with  a  fine  white  mealy  wax ;  it  collects  in  great  numbers 
on  the  under  side  of  the  leaves  of  tender  shoots  in  May  and  June. 
Spray  with  6  pounds  of  fish  oil  soap  to  200  gallons  of  water,  or  use 
nicotine  soap  spray  (Formula  27).  The  soap  alone  appears  to  give 
as  satisfactory  results  as  the  nicotine  soap  spray  and  is  much  cheaper. 

Peach  Twig  Borer. — See  "Peach." 

Pear  Thrips.— See  "Pear." 

Red  Spider  or  Almond  Mite. — See  "Almond." 

San  Jose  Scale. — See  "Apple." 

Tent  Caterpillars. — See  "General  Subjects." 

Two-Spotted  Mite,  Tetranychus  telarins  Linn. — This  small,  pale 
green  or  yellow  mite,  with  from  two  to  six  dark  spots  on  its  back, 
appears  in  mid  and  late  summer  and  does  great  damage  to  plum  and 
prune  trees  by  causing  the  leaves  to  fall  prematurely.  Dusting  and 
spraying  as  recommended  for  the  almond  mite  (see  "Almond")  should 
be  done  very  thoroughly  and  continued  until  the  first  good  rains  occur 
in  the  fall. 

Tussock  Moth.— See  "Apple." 

Combined  Spraying 
For  scale,  moss,  and  a  general  clean-up,  spray  in  winter  with  crude 
oil  emulsion  (Formula  26). 

POTATO 

Wilt,  Fusarium  sp. ;  Dry  Rot,  Fusarium  sp. ;  Scab,  Actinomyces 
scabies  (Thaxt.)  G\iss.  =  Oospor  a;  Rhizoctonia  or  Black  Scurf,  Cor- 
ticium  pagum  B.  &  C.  =  Rhizoctonia. — Wilt  affects  plants  like  a  severe 
drought,  causing  a  premature  ripening  of  the  leaves;  tubers  appear 
sound,  but  are  mostly  infected,  as  is  the  soil.  Dry  rot,  associated  with 
wilt  in  part,  is  retarded  by  cool  storage.  Scab  is  a  soil  infection  said 
to  be  favored  by  alkaline  soil  or  the  application  of  lime  or  manure  in 
excess,  and  retarded  by  recently  plowed  under  green  cover  crop. 
Rhizoctonia  appears  on  tubers  as  dark  scabs,  which  can  be  scraped  off, 
leaving  the  skin  unbroken ;  under  some  conditions  it  causes  the  dying 
of  young  stems  under  ground.  Obtain  clean  seed  from  healthy  plants. 
Discard  any  which  show  decided  dark  brown  discoloration  or  decay 
at  stem  end  to  a  depth  of  at  least  one-quarter  inch  from  the  end.  Soak 
the  seed  before  cutting  for  one  and  one-half  hours  in  a  solution  of 


36  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

1-1000  corrosive  sublimate  (1  ounce  to  8  gallons  of  water),  or  for  2 
hours  in  formaldehyde,  1  pound  to  30  gallons  of  water.  Use  a  wooden 
vessel  for  the  sublimate  and  have  the  tubers  as  clean  as  possible. 

Jelly  End,  Soft  Rot. — Infection  in  wounds  with  several  fungi, 
Pythium,  Rhizopus,  etc.    Avoid  injury  and  bruising  in  digging. 

Potato  Late  Blight,  Late  Rot,  Pkytophthora  infestans  (Mont.) 
De  Bary. — Translucent  spots  appear  on  the  leaves  and  stems,  which 
spread  rapidly  till  entire  top  is  wilted  and  prostrate.  The  tubers  show 
sunken  spots  at  digging  and  rot  in  storage.  Spray  with  Bordeaux 
mixture  (Formula  9)  immediately  after  rains. 

Aphids  (Various  Species). — Dust  thoroughly  with  5  per  cent  nico- 
dust  or  spray  with  1  part  of  40  per  cent  nicotine  sulfate  to  800  parts 
of  water. 

Armyworms  and  Cutworms. — See  "General  Subjects." 

Flea  Beetles  and  Leaf  Beetles. — See  "Melon."  Use  Bordeaux 
mixture  (Formula  9)  as  a  repellent,  or  a  nicodust  lead  arsenate 
mixture. 

Garden  Nematode  or  Eelworm. — This  animal  produces  a  pimply 
or  warty  surface  on  the  potato  and  small  brown  dots  just  beneath  the 
skin.    Plant  only  clean  seed  and  avoid  infested  soil. 

Grasshoppers. — See  "General  Subjects." 

Potato  Stalk  Borer,  Trichobaris  trinotata  Say. — The  larvae  are 
small,  pale  yellow  or  white,  and  not  over  one-half  inch  long ;  they  bore 
throughout  the  middle  of  the  stalks,  causing  them  to  wilt  and  die. 
The  adults  hibernate  in  the  old  dry  stalks,  which  should  be  raked  up 
after  digging  and  burned.  This  affords  an  almost  perfect  control  if 
thoroughly  done. 

Potato  Tuber  Moth,  Phthorimaea  operculella  (Zeller). — The  full- 
grown  caterpillars  are  white  or  pinkish  and  not  over  three-quarters 
inch  long.  They  make  numerous  burrows  just  under  the  skin  and 
throughout  the  tubers,  continuing  to  work  as  long  as  the  tubers  are 
available.  Infestation  may  occur  in  the  field  or  in  storage.  Hill  up 
well  around  the  growing  plants  and  remove  the  potatoes  as  soon  as 
dug  to  prevent  infestation  in  the  field.  Store  in  a  clean,  uninfested 
place.  If  infested,  fumigate  with  20  to  30  pounds  of  carbon  bisulfide 
to  every  1000  cubic  feet  of  air  space  at  a  temperature  70°  F.  or  over. 
Plant  only  clean  seed. 

Tomato  and  Tobacco  Worms. — See  "Tomato." 
Wireworms. — See  "General  Subjects." 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  37 

Combined  Spraying 
Bordeaux  mixture  will  control  not  only  the  flea  beetles  but  will 
materially  aid  in  subduing  many  fungus  diseases. 

PUMPKIN.    See  "Melon" 

ROSE 

Mildew,  Sphaerotheca  pannosa  (Wallr.)  Lev.  and  8.  humuli  (D.  C.) 
Burr.  =  Oidium. — White  powdery  mildew  spreads  over  young  stems 
or  leaves,  causing  distortion  or  dropping  of  leaves  and  discoloration ; 
severe  in  cool  coast  districts.  Spray  with  lime-sulfur  1-10  before  the 
spring  growth  starts.  Use  dry  sulfur,  sulfur  paste,  or  lime-sulfur  1-35 
when  disease  first  appears. 

Aphids  (Various  Species). — Two  common  aphids  usually  infest 
roses:  the  large  green  and  pink  Macrosiphum  rosae  (Linn.),  which 
commonly  attacks  the  tender  tips  and  buds,  and  the  small  green 
Myzaphis  rosarum  (Walk.),  which  works  on  all  parts  of  the  plant  and 
produces  large  quantities  of  honey  dew,  resulting  in  the  smutting  of 
the  plants.  Both  may  be  effectually  controlled  by  dusting  liberally 
with  5  per  cent  nicodust,  by  spraying  with  nicotine  sulfate,  40  per 
cent,  one  part  to  1000  parts  of  water,  or  by  thoroughly  hosing  off  the 
plants  every  two  or  three  days  with  a  strong  water  pressure  and  a 
coarse  nozzle. 

Fuller's  Rose  Beetle.— See  "Citrus  Fruits." 

Raspberry  Horntail. — See  "Bush  Fruits." 

Rose  Scale. — See  "Bush  Fruits."  Spray  infested  portions  of  the 
plants  during  the  winter  months  with  miscible  oils. 

Rose  Snout  Beetle,  Rhynchites  bicolor  Fabr. — A  small  red  and 
black  snout  beetle,  scarcely  one-quarter  inch  long,  which  punctures  the 
buds  of  roses,  causing  numerous  holes  in  the  petals  when  the  flowers 
open.  Jar  beetles  in  pan  of  oil  in  the  early  mornings.  A  10  per  cent 
nicodust  has  given  good  control  in  some  places. 

Combined  Spraying 
For  fungus  diseases  and  aphids,  a  40  per  cent  nicotine  sulfate  may 
be  added  to  sulfur  sprays  as  given  above,  and  a  sulfur  nicodust  may 
also  be  used  for  mildew  and  aphis. 


38  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

SNAPDRAGON 

Rust,  Puccinia  antirrhini  D.  &  H. — Brown  rust  sori  break  out 
through  the  leaf  and  stem.  Infection  is  usually  heavy  and  the  plant 
becomes  unsightly  and  dies.  Water  and  fertilize  freely  to  stimulate 
growth.  Destroy  badly  affected  plants  and  clean  up  thoroughly  in  the 
fall.  Pentstemon  is  a  fairly  good  substitute  for  snapdragon,  and  does 
not  rust. 

Aphids. — Dust  thoroughly  with  5  per  cent  nicodust. 

SORGHUM,  SUDAN  GRASS,  AND  BROOM  CORN 

Head  Smut,  Sphacelotheca  reiliana  (Kiihn.)  Clint. — Whole  head 
or  panicle  becomes  a  black  mass.  Method  of  treatment  not  yet  devel- 
oped. Affected  plants  should  be  destroyed  at  first  appearance.  Affects 
also  corn. 

Kernel  Smut,  Sphacelotheca  sorghi. — Kernels  form  enlarged  grains 
which  become  fragile  and  filled  with  a  black  powder.  Controlled  by 
seed  treatment.     See  "Grain." 

Aphids  (Various  Species). — See  "Grain." 

Armyworms  and  Cutworms. — See  "General  Subjects." 

Granary  and  Rice  Weevils. — See  ' '  Grain. ' ' 

Grasshoppers. — See  "General  Subjects." 

SPINACH 

Armyworms  and  Cutworms. — See  "General  Subjects."  Poisoned 
bran  mash  sown  broadcast  over  the  fields  has  proved  very  successful 
in  completely  protecting  young  plants. 

Beet  or  Spinach  Leaf  Miner,  Chortophila  hyoscyami  Panzer. — 
Small  white  maggots  mining  the  leaves  and  causing  discolored  areas. 
Keep  down  all  weeds  about  the  fields,  burn  refuse  tops,  harvest  as  early 
as  possible.  Winter  grown  spinach  usually  escapes  the  attacks  of  this 
insect. 

Flea  Beetles.— See  "Melon." 

Grasshoppers. — See  "General  Subjects." 

Melon  Aphis.— See  "Melon." 

SQUASH.    See  Melon 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  39 

STRAWBERRY 

Leaf  Spot,  Mycosphaerella  fragariae  (Tul.)  Linn.  =  Ram ularia. — 
Dead  spots  on  leaves,  one-quarter  inch  or  less  in  diameter  with  red 
borders ;  if  abundant  it  lowers  the  vitality  of  the  plants.  Clean  up 
and  burn  the  leaves  in  late  fall.  Spray  with  Bordeaux  mixture 
(Formula  9)  if  the  disease  becomes  serious. 

Leaf  and  Stem  Rot. — Symptoms  are  those  of  acute  drought  injury ; 
plants  die  back  in  hot  weather  and  inferior  growth  comes  up  later  with 
poor  production ;  roots  are  killed  off,  apparently  by  poor  soil  conditions. 
Use  less  water.  Improve  drainage.  Wash  out  alkali  in  winter  by 
flooding. 

Gray  Mold,  Botrytis  rot. — See  "Bush  Fruits." 

Strawberry  Aphis,  Myzus  fragaefolii  Ckll. — A  very  small  pale 
yellow  aphis  occurring  in  great  numbers  on  the  under  sides  of  the 
leaves,  and  often  smutting  the  foliage.  Defoliate  the  plants  in  winter. 
Dust  liberally  with  5  per  cent  nicodust  as  soon  as  the  aphids  appear, 
applying  it  to  the  under  side  of  the  leaves  with  an  upturned  discharge 
pipe. 

Strawberry  Crown  Moth,  Aegeria  rutilans  H.  Edw. — A.white  cater- 
pillar one-half  inch  long  or  less  boring  in  to  the  crown  of  the  plant, 
causing  it  to  turn  yellow  and  die.  Remove  and  burn  infested  plants 
as  soon  as  discovered.    Be  sure  of  clean  nursery  stock. 

Strawberry  Flea  Beetle,  Haltica  ignita  Illiger. — A  bright  metallic, 
golden,  green,  or  purplish  flea  beetle,  one-sixth  inch  long,  feeding  upon 
the  leaves  of  the  plants.  Use  Bordeaux  mixture  (Formula  9)  as  a 
repellent. 

Strawberry  Leaf  Beetle,  Typophorus  canellus  (Fabr.). — A  small 
brown  beetle  with  black  markings  on  the  dorsum  and  averaging  one- 
eighth  inch  long.  The  adults  eat  numerous  small  irregular  holes  in 
the  leaves,  while  the  small  white  larvae  attack  the  roots.  It  is  a  severe 
pest,  and  should  be  eradicated,  if  possible,  by  destroying  all  infested 
vines  and  thoroughly  sterilizing  the  soil  by  steam  or  carbon  bisulfid. 
Established  infestations  may  be  reduced  by  thoroughly  spraying  with 
arsenate  of  lead  (Formula  2),  or  by  dusting  with  1  part  of  basic 
powdered  arsenate  of  lead  to  4  parts  of  powdered  hydrated  lime. 

Strawberry  Root  Weevil. — The  one  known  infestation  of  Oiio- 
rhynchiis  rugifroms  Gyll.  in  California  is  quarantined.  Secure  plants 
from  uninfested  district.  Report  any  suspicious  cases  to  the  State 
Department  of  Agriculture,  Sacramento,  Calif. 


40  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Two-Spotted  Mite,  Tetranychus  telarius  Linn. — See  "Bean"  and 
"Prune."  Though  ordinarily  controlled  with  dry  sulfur,  this  method 
cannot  be  used  on  strawberries  because  of  the  severe  burning  to  the 
foliage.  Very  small  amounts  of  sulfur  in  the  ditches  between  the  rows 
have  afforded  some  relief. 

SWEET  POTATO 

Soft  Rot,  Rhizopus  nigricans  Ehr. — Mainly  a  storage  trouble ;  rot 
starts  at  injuries  and  progresses  rapidly ;  decayed  part  becomes  cov- 
ered with  white  mold  which  later  turns  black.  Avoid  bruising.  Dry 
well  before  storing.  For  long  keeping,  pack  in  dry  sand.  Moisture 
and  temperature  requirements  of  sweet  potatoes  in  storage  are  different 
from  those  of  most  other  products  and  must  be  carefully  observed. 

Wilt,  Fusarium  sp.,  Black  Rot,  Ceratocystis  fimbriata  (E.  &  II.) 
Sacc. — Wilt  affects  growing  plants  in  the  field.  Black  Rot  forms  dark 
patches  of  dry  rot  which  begin  development  in  the  field  and  continue 
in  storage.  Infected  potatoes  are  bitter.  Get  clean  seed  potatoes  from 
an  uninfected  locality.    Destroy  diseased  vines  after  digging. 

TOBACCO.     See  "Tomato" 

TOMATO.     See  also  < '  Potato ' ' 

Blossom  End  Rot. — Dry  spot  appears  at  blossom  end  of  green  fruit 
and  develops  slowly.    Avoid  drought  or  irregular  irrigation. 

Damping-off. — See  "General  Subjects." 

Late  Blight,  Late  Rot,  Phytophthora  infestans  (Mont.)  De  B. — In 
late  moist  weather  large  vague  spots  appear  on  the  leaves,  at  first  dark 
and  watery,  becoming  slightly  frosted  with  emerging  fungus  threads 
below,  then  deteriorating  rapidly.  Similar  spots  appear  on  the  fruit, 
not  well  marked  at  first,  but  the  fruit  spoils  rapidly.  Spray  with 
Bordeaux  mixture  (Formula  9)  immediately  after  rains. 

Wilt,  Summer  Blight. — Plants  become  pale,  leaves  roll  upward, 
exposing  purplish  veins,  plants  become  worthless  and  most  of  them  die. 
Use  plants  free  from  damping-off.  Replant  if  not  too  late.  Cannot 
be  controlled  in  some  years. 

Armyworms  and  Cutworms. — See  "General  Subjects." 

Grasshoppers. — See  "General  Subjects." 

Darkling  Ground  Beetles,  Blapstinus  sp.  and  Eurymetopon  hicolor 
Horn. — Small,  dull  black  or  bluish-black  beetles,  scarcely  more  than 
one-quarter  inch  long,  living  in  the  soil  and  responsible  for  much  dam- 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  41 

age  to  young  plants  shortly  after  transplanting.  Before  resetting, 
wrap  the  stems  of  the  young  plants  from  roots  to  tops  with  tissue  paper 
so  as  to  have  three  or  four  thicknesses  for  protection,  or  scatter  poison 
bran  mash  (Formula  4)  over  the  ground  at  planting  time. 

Flea  Beetles. — Dust  with  powdered  arsenate  of  lead,  1  part  to  4 
parts  of  dry  lime  or  sulfur,  nicodust  and  arsenate  of  lead,  or  spray 
with  Bordeaux  mixture  (Formula  9). 

Garden  Nematode. — See  "General  Subjects." 

Tomato  Worm,  Protoparce  sexta  Joh.  and  Tobacco  Worm,  P.  quin- 
quemaculata  Haw. — Large  green  worms  often  attaining  a  length  of 
four  inches.  They  strip  the  leaves  from  the  vines.  The  adults  are 
known  as  humming  bird  moths  because  of  their  large  size  and  swift 
flight.  They  are  gray  with  yellow  spots  on  the  sides  of  the  body  and 
have  a  wing  expanse  of  4  or  5  inches.  The  caterpillars  may  be  con- 
trolled by  hand  picking,  i.e.,  cutting  the  worms  in  two  with  a  pair  of 
scissors,  or  by  dusting  the  vines  with  1  part  of  powdered  arsenate 
of  lead  to  4  parts  of  finely  ground  hydrated  lime. 

WALNUT 

Blight,  Pseudomonas  juglandis  Pierce. — Young  tender  parts  are 
attacked.  Spots  at  first  watery,  soon  turning  black,  often  spread  and 
kill  young  nuts,  leaves,  or  tender  tips  of  shoots.  No  specific  remedy. 
Give  the  trees  the  best  possible  care.  Thin  out  the  tops  of  the  old  trees. 
Control  aphis.    Plant  resistant  varieties. 

Crown  Gall,  Wood  Decay,  Armillaria. — See  "General  Subjects." 

Melaxuma,  Dothiorella  gregaria  Sacc. — Black  sunken  cankers  de- 
velop on  larger  limbs  and  trunks;  the  limb  may  be  girdled  and  the 
part  above  die.    Cut  out  diseased  bark  areas  and  apply  Bordeaux  paste. 

Winter  Killing. — Irrigate  about  November  1,  if  no  good  rains  have 
fallen.  Whitewash  trunks  in  the  fall.  Do  not  irrigate  after  August, 
except  as  above. 

Codling  Moth,  Cydia  pomonella  (Linn.). — See  "Apple."  This 
worm  feeds  on  the  green  husks  or  usually  bores  directly  into  the  kernel 
of  the  walnuts  before  they  are  mature,  and  also  often  works  its  way 
into  the  kernel  after  the  shell  becomes  hardened  by  making  an  entrance 
in  the  suture  at  the  base.  It  may  be  controlled  by  spraying  with  basic 
arsenic  of  lead  or  by  dusting  with  powdered  basic  arsenate  of  lead  and 
hydrated  lime  when  work  on  husks  of  nuts  is  first  observed  in  the 
spring — May,  June,  or  July — depending  upon  climatic  conditions  due 
to  location  near  the  coast  or  inland.  Consult  local  horticultural  officials. 


42  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Frosted  Scale,  Lecanium  pruinosum  Coq.,  and  Cherry  or  Calico 
Scale,  L.  cerasorum  Ckll. — Same  control  as  for  brown  apricot  scale. 
See  "Apricot." 

Indian  Meal  Moth. — Attacks  walnuts  in  storage.    See  "Prune." 

Nautical  Borer,  Xylotrechus  nauticus  Mann. — The  borers  are  small, 
fleshy,  white  or  yellowish  grubs,  with  slightly  enlarged  anterior  end, 
and  about  three-quarters  inch  long.  The  adult  beetles  are  one-half 
inch  long,  dark  with  narrow  broken  yellow  or  whitish  cross  bands  on 
the  elytra.  The  larvae  work  in  the  small  twigs,  limbs,  and  trunks  of 
both  healthy  and  sickly  trees.  Cut  out  and  burn  all  infested  portions. 
Destroy  all  dead  oaks  or  prunings  in  the  neighborhood  to  eliminate 
breeding  places. 

Red  Humped  Caterpillar. — See  "Prune." 

Two-Spotted  Mite. — See  "Prune."  Dust  thoroughly  with  dry 
sulfur. 

Walnut  Aphis,  Chromaphis  juglandicola  (Kalt.). — A  small  pale 
yellow  aphis  occurring  in  great  numbers  on  the  under  sides  of  the 
leaves  and  producing  great  quantities  of  honey  dew,  which  causes  severe 
smutting  of  the  foliage.  Dust  thoroughly  with  a  2  per  cent  nicodust 
during  last  week  of  May  or  the  first  part  of  June.  Sometimes  a  second 
application  is  necessary  in  July  or  August. 

Walnut  Blister  Mite,  Eriophyes  erinea  Nalepa. — A  microscopic 
mite  producing  yellow  or  brown  felt-like  galls  on  the  under  sides  of  the 
leaves.  It  is  not  a  serious  pest,  but  may  be  cleaned  up  by  spraying 
trees  with  lime-sulfur  1-10  in  the  spring  when  the  buds  are  swelling. 
Control  measures  are  not  recommended  except  in  extreme  cases. 

Yellow-Necked  Caterpillar,  Dot  ana  ministra  Drury. — A  black, 
hairy  caterpillar  with  numerous  longitudinal  yellow  stripes  on  the 
back  and  sides  and  a  yellow  or  orange-colored  neck.  It  averages  about 
two  inches  in  length  and  is  closely  related  and  similar  in  habits  to  the 
red  humped  caterpillar,  and  may  be  handled  in  the  same  way.  See 
same  under  "Prune." 

WATERMELON.    See  "Melon" 

WHEAT.     See  "Grain" 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  43 


GENERAL  SUBJECTS 

ANTS 

Ants  are  not  only  serious  household  pests  but  do  harm  in  the  garden 
and  orchard  by  distributing  plant  lice,  scale  insects,  and  other  honey- 
dew  producing  insects,  and  protecting  them  from  parasitic  enemies, 
which  would  otherwise  destroy  great  numbers  of  these  pests. 

The  ordinary  small  house  ants,  which  give  off  a  pungent  character- 
istic "ant"  odor  when  crushed,  are  best  controlled  by  using  various 
strong,  arsenic,  and  syrup  poisons  sold  as  ' '  ant  poisons. ' '  The  Argen- 
tine ant,  which  gives  off  no  characteristic  odor,  is  controlled  by  a  very 
weak  arsenic  and  syrup  poison  which  is  carried  to  the  young  by  the 
workers  and  which  gradually  kills  out  the  whole  colony.  For  this  pest 
use  Formula  7  or  8,  or  buy  special  Argentine  ant  poison. 

Home-made  containers  for  the  latter  poison  may  be  made  by  punch- 
ing small  holes  around  the  tight-fitting  tops  of  cans  and  then  dipping 
in  hot  paraffine  to  prevent  rusting.  A  sponge  is  placed  in  the  bottom 
and  thoroughly  wet  with  the  poison,  the  lid  is  securely  fastened,  the 
container  marked  ' '  Poison, ' '  and  then  hung  up  under  or  in  the  house, 
or  in  the  gardens  or  orchards,  away  from  the  reach  of  children.  Small 
fruit  jars  with  holes  punched  in  the  lids  may  be  used  instead  of  cans, 
and  if  screwed  very  tightly  are  less  likely  to  be  opened  by  children. 

ARMILLARIA  ROOT  ROT  (OAK  FUNGUS),  Armillaria  mellea 

(Vahl.)  Quel. 

Caused  by  a  native  fungus  which  lives  saprophytically  and  para- 
sitically  in  roots  of  woody  plants.  Trees  and  bushes  are  killed  in  spots, 
which  enlarge  year  after  year.  Affected  trees  fail  gradually  from  dis- 
eased side  or  die  suddenly  in  summer.  Under  the  affected  bark  of  roots 
there  is  a  yellowish  white  fan-shaped  mycelium  which  progresses  into 
live  bark.  Black  shining  root-like  strings  (rhizomorphs)  grow  out 
from  old  rotting  roots.  The  wood  decays  with  a  uniform  white  rot. 
Large  tan-brown  toadstools  (edible  when  cooked)  arise  from  old 
infections,  October  to  February.  Surgery  as  in  Crown  Gall  or  Pear 
Blight  can  sometimes  be  practiced  on  roots  and  crowns  of  trees  not  too 
far  gone.  Black  walnut,  French  pear,  and  fig  roots  are  practically 
immune.  Annual  fibrous  rooted  plants  are  rarely  injured.  Affected 
areas  in  orchard  may  be  isolated  by  opening  a  trench  3  to  4  feet  deep 


44  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

around  them.  This  may  be  filled  immediately  if  reopened  every  two 
years  to  keep  the  roots  cut  off.  Nursery  should  not  be  planted  in  in- 
fected soil. 

ARMYWORMS  AND  CUTWORMS 

General  Life  History. — The  adult  members  of  this  family  (Noc- 
tuidae)  are  practically  all  night-flyers.  The  caterpillars  of  many  are 
known  as  armyworms  and  cutworms  and  are  among  the  most  destruc- 
tive of  insect  pests.  They  often  advance  from  field  to  field  in  great 
numbers,  like  an  army,  devastating  as  they  go.  Like  the  grasshoppers, 
they  attack  practically  all  kinds  of  plants,  including  field  and  truck 
crops,  vineyards  and  orchards,  as  well  as  flowers  and  weeds. 

The  adults  lay  their  eggs  in  spring  and  the  larvae  become  exceed- 
ingly numerous  in  early  summer,  when  most  of  the  damage  is  done. 
The  pupal  stage  is  passed  under  ground,  the  light  or  dark-brown  naked 
chrysalids  being  housed  in  small  earthen  cells.  There  are  several  broods 
a  year.  The  winter  is  usually  spent  in  the  pupal  stage,  but  some  larvae 
as  well  as  adults  hibernate.  A  hibernating  larva  often  seriously  injures 
grapevines  in  the  spring  by  eating  the  buds. 

Control. — The  control  of  these  insects  has  been  a  difficult  problem 
for  years,  and  even  today  the  methods  worked  out  do  not  always  give 
relief. 

Clean  culture  in  fall  and  thorough  plowing  of  infested  fields  to 
kill  the  hibernating  pupae  in  the  cells  is  supposed  to  greatly  reduce 
the  next  year 's  broods.  This  has  been  recommended  as  especially  im- 
portant in  pea  fields  and  gardens. 

"When  the  worms  begin  to  march  trenches  may  be  plowed  across 
and  ahead  of  their  paths  with  a  perpendicular  wall  in  front  of  the 
advance.  The  worms,  not  being  able  to  cross,  will  gather  in  great 
masses  in  these  trenches  and  can  be  easily  killed  by  spraying  with  crude 
oil  or  by  crushing  them  with  a  narrow  disk  or  roller.  Arsenical  sprays 
applied  as  soon  as  the  larvae  begin  to  appear  will  sometimes  materially 
aid  in  protecting  crops  like  potatoes,  tomatoes,  young  trees,  grapevines, 
etc.,  but  are  seldom  practical  for  forage  crops. 

Poisoned  baits  (Formulas  4  and  5)  sown  in  the  infested  fields  will 
kill  countless  worms,  and  these  afford  by  far  the  most  satisfactory 
means  of  killing  these  insects  under  all  conditions.  In  fields,  pastures, 
orchards,  and  gardens,  the  poisoned  baits  may  be  freely  sown  over  the 
plants.  The  armyworms  and  cutworms  will  eat  the  bait  in  preference 
to  growing  vegetation. 

Light  traps  are  also  used  to  capture  the  adults,  but  these  have  never 
seemed  to  greatly  lessen  the  attacks,  because  large  numbers  of  the  moths 
captured  have  previously  laid  their  eggs. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  45 

Natural  Enemies. — By  far  the  most  important  factors  in  the  con- 
trol of  armyworms  and  cutworms  are  natural  enemies.  The  parasitic 
tachinid  flies  kill  countless  numbers  of  them.  Hymenopterous  para- 
sites of  the  family  Ichneumonidae  also  prey  upon  the  young.  The 
predaceous  ground  beetles  of  the  family  Carabidae  devour  the  worms 
and  destroy  great  numbers.  That  armyworms  and  cutworms  are  not 
injurious  every  year  is  undoubtedly  due  to  the  work  of  these  natural 
enemies. 

CANKERWORMS 

Small  green  or  dark  measuring  worms  less  than  an  inch  long,  which 
feed  upon  the  leaves  and  young  fruit  and  drop  down  on  a  silken  thread 
when  the  tree  is  jarred.  The  females  are  wingless  and  crawl  up  the 
trees  in  the  fall  or  spring  to  lay  their  eggs  on  the  limbs  and  small 
branches.  Egg-laying  on  the  trees  is  prevented  by  placing  tanglefoot, 
cotton,  or  permanent  wire  screen  bands  around  the  trunks  of  the  trees 
in  the  fall  in  order  to  catch  both  the  fall  and  spring  forms.  The  cater- 
pillars are  easily  jarred  from  the  trees,  but  will  crawl  up  again  if  not 
obstructed.    Spraying  with  arsenate  of  lead  (Formula  4)  will  also  give 

CROWN  GALL,  Bacterium  tumefaciens  S.  &  T. 
Rounded  fleshy  to  woody  tumors  form  on  roots  or  sometimes  on 
above-ground  parts,  usually  starting  from  wounds,  persisting  and 
growing  at  the  edges  from  year  to  year,  often  girdling  or  causing  the 
tree  to  break  off.  For  nurseries,  avoid  old  vineyard,  orchard,  or  berry 
land  which  has  been  seriously  infected.  Throw  out  all  affected  nursery 
trees.  The  clean  trees  in  a  lot  having  a  large  percentage  affected  are 
of  doubtful  value.  In  orchards,  occasionally  examine  crown  and  main 
roots,  especially  of  stunted  trees.  When  not  too  far  advanced  this 
disease  may  be  controlled  by  chiseling  out  the  galls,  removing  all  ab- 
normal tissue  to  healthy  bark  and  down  to  sound  wood,  sterilizing  with 
corrosive  sublimate  (Formula  28  or  28a),  and  covering  the  wounds 
with  Bordeaux  paste  or  asphaltum.  The  trees  must  be  gone  over  again 
after  vigorous  growth  has  been  going  on  for  several  weeks  and  the  new 
galls  which  arise  at  the  wound  margins  treated.  Reinspection  is  essen- 
tial. Badly  affected  and  stunted  trees  should  be  pulled  out  and  re- 
planted, using  fresh  soil. 

DAMPING-OFF 

Young  seedlings  rot  at  or  below  the  surface  of  the  ground  and  fall 
over  or  wilt.  Many  may  die  before  emerging.  Cause,  various  soil 
fungi,  Pythium,  Rhizoctonia,  Fusarium,  and  others.     Best  controlled 


46  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

by  skill  in  watering.  Water  the  plant  beds  only  in  the  morning  and 
on  bright  days.  Do  not  sprinkle  oftener  than  necessary.  In  green- 
houses or  frames  give  plenty  of  ventilation.  In  making  citrus  seed 
beds  put  an  inch  or  two  of  dry  sand  on  the  top  of  the  soil.  Some  forms 
of  Damping-off  can  be  prevented  by  steam-sterilizing  the  soil  before 
planting,  or  by  drenching  with  a  solution  of  4  pounds  of  formaldehyde 
in  50  gallons  of  water,  using  1  gallon  of  solution  to  every  square  foot. 
This  must  be  done  two  weeks  in  advance  so  that  no  odor  of  formalde- 
hyde remains  at  planting  time.  Where  damping-off  has  started, 
spraying  the  plants  and  ground  with  Bordeaux  may  do  some  good. 

FLIES 

Should  be  prevented  from  breeding  by  keeping  manure,  garbage, 
and  similar  refuse  material  covered  tightly.  For  poisoning  flies  in  the 
house,  use  about  2  per  cent  formaldehyde  solution  exposed  in  saucers, 
adding  a  little  sugar. 

FROST  AND  COLD  INJURY 

With  young  citrus  trees  in  frosty  localities,  wrap  the  trunks  with 
corn  or  milo  stalks  in  winter.  Heap  up  earth  around  the  butts.  En- 
close tender  valuable  young  trees  with  burlap  covers.  For  bearing 
groves  obtain  detailed  information  about  methods  and  appliances  for 
smudging  with  oil  fuel.  (See  also  Sour  Sap.)  Many  plants  are  injured 
and  disfigured  by  cold  at  critical  stages  of  development,  even  when  it 
is  not  cold  enough  to  kill  or  even  noticeably  injure  them  at  the  time. 

GRASSHOPPERS 

Scatter  poison  bran  mash  or  citrus  bran  mash  freely  (Formula  4 
or  5).  Be  sure  to  mix  the  bran  and  poison  thoroughly.  Scatter  in 
alfalfa  fields  about  4  o'clock  in  the  afternoon  and  around  orchard  trees 
or  other  plants  early  in  the  morning. 

GUMMOSIS 

Gum  formation  in  itself  is  not  due  to  any  one  specific  disease,  but 
may  be  brought  about  by  many  different  causes.  In  stone  fruit  and 
citrus  trees  gumming  is  simply  a  symptom  of  distress,  which  may  be 
due  to  specific  infections  or  various  other  causes,  such  as  unsuitable 
soil,  poor  condition  of  soil,  sunscald,  excess  or  lack  of  water,  frost, 
or  attacks  of  parasites.  Treatment  must  vary  according  to  cause. 
Badly  gummed  branches  may  be  removed,  gummy  diseased  areas  of 
bark  cut  out,  and  the  wounds  treated  as  in  citrus  gummosis.  Splitting 
the  bark  is  useless  and  often  harmful. 


Circular  227]  plant  disease  and  pest  control  47 

NEMATODE  (EEL  WORM) 

Microscopic  worms  of  several  species  penetrate  the  tender  tissues 
of  plants.  The  garden  nematode  causes  rounded  irregular  fleshy  swell- 
ings or  root  knots  on  tender  roots.  If  abundant,  the  roots  may  become 
much  distorted  and  swollen,  growth  stops,  and  early  rotting  off  follows. 

Do  not  attempt  to  grow  susceptible  crops  on  infested  soil.  Keep 
such  areas  clean  cultivated  in  summer  or  in  a  cereal  crop.  Grain  may 
be  grown  in  winter.  Almost  all  important  crops,  except  cereals  and 
some  fruit  trees,  are  attacked  by  the  garden  nematode.  The  beet 
nematode  attacks  some  other  plants,  and  where  it  occurs  careful  rota- 
tions should  be  followed  with  total  exclusion  of  beets  for  many  years. 
Alfalfa  is  not  seriously  affected  by  the  common  species,  but  carries  it 
over  to  future  crops.  Alfalfa  may  be  safely  planted  on  beet  nematode 
soil.    Nematodes  are  worse  on  sandy  soils. 

PHYSIOLOGICAL  DISEASES 

(Little  Leaf,  Exanthema,  Die-Back,  Mottled  Leaf,  Rosette,  Bitter  Pit, 
Dry  Rot,  Blossom-End  Rot) 

Diseases  of  a  specific  nature  of  which  the  cause  is  not  known  and 
of  which  the  symptoms  seem  unlike  the  usual  effects  of  unfavorable 
conditions  or  parasites.  Most  of  these  troubles  show  a  relation  to  soil 
conditions  and  occur  especially  in  dry,  sandy,  gravelly,  or  hardpan 
soils,  those  very  deficient  in  humus,  or  under  conditions  of  irregular 
soil  moisture.  Trees  standing  over  old  barnyards  or  corrals  or  where 
excessive  amounts  of  manure  have  been  applied  are  also  likely  to  show 
some  of  these  troubles.  The  most  promising  methods  of  treatment  are 
increasing  the  humus  content  of  the  soil  by  means  of  green  manure 
crops  and  mulches,  breaking  up  all  hardpan  and  plow-soles,  more  care- 
ful irrigation  to  insure  the  maintenance  of  a  proper  and  uniform 
moisture  condition  of  the  soil  down  to  a  depth  of  several  feet  and 
throughout  the  season  until  rains  occur,  and  planting  alfalfa  in  orch- 
ards where  plenty  of  water  is  available.  The  soil  in  areas  where  these 
troubles  occur  should  be  examined  for  alkali  or  other  injurious  sub- 
stances. Where  any  of  these  diseases  are  serious  and  persistent  it  may 
be  better  to  grow  some  other  crop  than  to  keep  on  with  one  which  is 
seriously  affected. 

RABBITS 

If  very  abundant,  must  be  fenced  out  of  young  orchards  and  gar- 
dens to  avoid  serious  damage.     Shooting  and  poisoning  are  the  prin- 


48  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

cipal  means  of  destruction.  An  application  of  whitewash  containing 
bitter  aloes  to  the  trunks  of  young  trees  is  sometimes  recommended, 
but  this  has  not  shown  much  value  in  actual  practice. 

Soaked,  chopped  alfalfa  sprinkled  with  strychnine,  Paris  green  or 
white  arsenic  is  very  effective  in  destroying  cotton-tails. 

SLUGS  AND  SNAILS 

May  be  controlled  to  some  extent  by  thoroughly  dusting  finely 
powdered  hydrated  lime  over  the  infested  plants,  but  recent  investi- 
gations have  shown  that  a  5  per  cent  nicodust  is  very  effective  in  killing 
these  pests  if  applied  late  in  the  evening  or  on  dull  days  when  the 
animals  are  at  work  on  the  plants.  Trapping  by  means  of  boards  or 
wet  sacks  and  killing  those  taking  shelter  thereunder  is  effective  in  a 
small  way. 

SOUR  SAP,  WINTER  INJURY.     Also  see  "Sunburn" 

All  the  ordinary  forms  of  sour  sap  are  due  to  extreme  variations  in 
temperature.  Differences  in  the  effect  upon  individual  trees  or  orch- 
ards are  due  to  differences  in  condition  and  susceptibility  of  the  trees, 
produced  mostly  by  variation  in  the  moisture  condition  of  the  soil. 
Do  not  force  growth  late  in  summer.  Irrigate,  if  possible,  about  No- 
vember 1,  if  no  heavy  rain  has  fallen.  Whitewash  bodies  of  trees  early 
in  November.  Sour  sap  seems  to  be  associated  with  hardpan  or  periods 
of  surplus  water  in  the  soil.  Good  drainage  should  be  emphasized.  A 
furrow  may  be  opened  in  early  winter  on  either  side  of  the  tree  row 
to  carry  off  surplus  winter  rains  and  prevent  the  soil  from  remaining 
saturated  for  prolonged  winter  periods.  Numerous  instances  have  been 
observed  where  open  irrigation  ditches  have  drained  adjacent  tree  rows 
during  the  winter.  Trees  in  the  drained  soil  have  escaped  sour  sap 
while  those  farther  from  the  ditch  in  soil  saturated  with  winter  water 
have  suffered  badly. 

SQUIRRELS  AND  GOPHERS 

May  be  controlled  by  persistent  poisoning,  fumigation  with  carbon 
bisulfide,  trapping  and  shooting.  For  poisoning  material,  the  commer- 
cial preparations  may  be  used  or  Formula  33. 

Poisoned  Fruit. — Strychnine  sulfate  may  be  sprinkled  over  orange 
halves  or  watermelon  rind,  or  a  solution  of  1  ounce  of  strychnine  sulfate 
dissolved  in  1  gallon  of  boiling  water  may  be  used  for  saturating  grain 
or  other  material,  after  allowing  the  solution  to  cool. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  49 

SUNBURN 

Whitewash  bodies  in  fall  as  well  as  spring.  Shape  the  trees  so  that 
their  trunks  are  shaded.  Cut  young  trees  back  well  before  planting. 
Shade  trunks  with  shakes  or  protectors.  Do  not  allow  trees  to  suffer 
from  drought. 

Tests  show  that  the  coloring  matter  in  the  bark  of  the  trunk  and 
exposed  main  limbs  absorbs  heat  enough  on  sunny  days  in  winter  to 
raise  the  temperature  of  the  growing  layer  35°  to  40°  F.  above  the 
temperature  of  the  air.  As  soon  as  the  sun  goes  down  the  tree  cools 
rapidly  to  atmospheric  temperature,  which  may  be  freezing  or  below. 
Whitewash  reflects  the  heat,  so  that  the  growing  layer  does  not  get 
warmer  than  the  air,  the  cells  remain  dormant  during  the  day,  and  are 
not  injured  by  low  temperatures  at  night.  The  above  also  applies  in 
opposing  sour  sap. 

TENT  CATERPILLARS 

Gray  or  brown,  hairy  caterpillars  with  row  of  white  spots  on  back 
or  pale  bluish  lines  on  sides,  measuring  from  1  to  3  inches  long.  They 
either  live  in  compact  colonies  or  in  tightly  woven  webs  or  tents  which 
are  conspicuous  on  the  trees.  Entire  colonies  may  be  exterminated  by 
cutting  off  or  burning  with  a  torch.  Those  on  the  trunks  and  large 
limbs  may  be  killed  by  spraying  with  kerosene  or  concentrated  oil 
emulsions.  The  small  dark  egg  masses  encircling  the  smaller  limbs 
may  be  pruned  out  when  the  trees  are  dormant  and  burned.  Spraying 
with  arsenate  of  lead  (Formula  1  or  2)  will  control  the  caterpillars 
effectually. 

TREE  WOUNDS,  PRUNING  CUTS 

Make  a  clean,  smooth  cut,  trimming  the  bark  down  smoothly  to 
sound  tissues  around  the  edges.  In  the  case  of  branches,  make  a  smooth 
cut,  leaving  no  projecting  stub.  Thoroughly  cover  the  wound  with 
Bordeaux  paste  (Formula  10),  and  after  callus  starts  to  form  about 
the  edges  cover  with  grade  D  asphaltum  put  on  in  a  melted  condition. 
Go  over  the  work  occasionally,  especially  in  summer  or  early  fall,  and 
renew  the  application  of  asphaltum  until  the  wound  is  entirely  healed. 
Bordeaux  mixture  retards  the  formation  of  callus  and  the  edges  of  the 
wound  may  be  covered  with  asphalt  first  to  protect  the  cambium  and 
the  Bordeaux  applied  later.  Some  prefer  to  paint  the  whole  wound 
at  once  with  hot  asphaltum.  Others  prefer  to  use  the  asphalt  paint 
cold,  but  this  should  be  done  with  care  to  keep  cracks  in  the  wood 
thoroughly  covered.  Paints  like  white  lead  and  oil,  which  harden  and 
may  crack,  can  not  be  recommended. 


50  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

WIREWORMS 

Wireworms  get  their  name  from  their  smooth,  round  bodies,  which 
are  usually  shiny,  varying  in  color  from  pale  yellow  to  dark  brown. 
The  common  injurious  forms  are  about  one  inch  long.  They  live  in 
the  soil,  preferring  sandy  loams  rather  than  heavy  soils,  although  they 
may  be  found  in  either.  The  larval  stages  last  from  1  to  3  years>  so 
that  to  be  effective  control  measures  must  cover  the  maximum  period. 
The  adult  beetles  are  known  as  "click  beetles "  because  of  their  ability 
to  jump  in  the  air  with  a  clicking  sound.  They  are  mostly  inconspic- 
uous beetles  of  various  shades  of  brown  or  entirely  black,  about  one- 
half  inch  long.    They  are  active  and  fly  freely. 

Control  measures  are  difficult  because  of  the  underground  habits 
of  the  larvae,  and  as  yet  have  not  been  satisfactorily  worked  out  for 
the  different  species.  Clean  culture  and  crop  rotations  are  the  most 
reliable  practices,  while  much  good  comes  from  thorough  cultivation. 
Trapping  the  adults  with  small  piles  of  straw  and  burning  them  in  fall 
and  winter  destroys  large  numbers.  Replanting  is  often  necessary 
with  many  crops  such  as  potatoes,  beans,  peas,  melons,  etc.  Some  con- 
trol is  claimed  from  scattering  poison  bran  mash  (Formula  4)  over  the 
surface  of  the  ground. 

FORMULAS  AND  DESCRIPTION  OF  MATERIALS 

ARSENICALS 

Acid  Lead  Arsenate  (Lead  Hydrogen  Arsenate,  Di-lea(i  Arsenate, 
Often  Labeled  "Standard"  or  Lead  Arsenate). — The  acid  type  of  lead 
arsenate  contains  more  poison  per  pound  than  the  basic  type,  is  a 
stronger  poison  and  acts  more  quickly.  It  is,  however,  somewhat  sus- 
ceptible to  the  action  of  other  chemicals,  particularly  those  of  an  alka- 
line nature  (such  as  soaps,  lime-sulfur  solution,  etc.),  and  is  more  or 
less  dissolved  by  them  when  used  as  a  combination  spray.  In  moist 
climates  along  the  coast,  or  in  continuous  damp,  cloudy  weather  else- 
where, whether  used  alone  or  in  combination  with  other  sprays,  some 
of  the  arsenic  is  apt  to  be  dissolved  and  to  cause  serious  foliage  injury. 
It  is  not  considered  a  safe  arsenical  for  use  on  stone  fruits,  beans,  or 
other  susceptible  plants. 

Basic  Lead  Arsenate  (Usually  Labeled  ' ' Tri-plumbic ' '  or  ' 'Neu- 
tral").— The  basic  type  of  lead  arsenate  is  a  weaker  poison  and  acts 
more  slowly.  It  is  not  decomposed,  however,  by  chemicals  of  an  alka- 
line nature,  such  as  are  usually  applied  with  it  as  a  combination  spray, 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  51 

nor  by  the  damp  weather  of  the  coast  regions.  It  is  considered  the 
only  safe  arsenical  to  use  on  stone  fruits,  beans,  or  other  susceptible 
plants. 

The  lead  arsenates  are  usually  sold  as  a  paste  containing  about 
50  per  cent  of  water,  or  as  a  dry  powder.  The  paste  should  be  thinned 
somewhat  with  water  and  worked  into  a  smooth  cream  before  adding  to 
the  spray  tank.  The  powder  may  be  added  directly  to  the  tank  and 
mixed  by  means  of  the  agitator. 

For  codling  moth  and  most  defoliating  insects  use : 

Formula  1 

Dry  acid  lead  arsenate  (paste,  4  to  8  pounds) 2  to  4  pounds 

Water - 100  gallons 

Or 

Formula  2 

Dry  basic  lead  arsenate  (paste,  5  to  10  pounds) 2%  to  5  pounds 

Water 100  gallons 

Dry  or  powdered  lead  arsenate  contains  twice  as  much  arsenic  as 
the  paste,  therefore  use  only  one-half  as  much  of  it. 

Zinc  Arsenite  is  a  stronger  and  more  active  poison  than  either  type 
of  lead  arsenate,  and  is  useful  in  controlling  the  various  caterpillars 
which  are  troublesome  on  pears  and  apples  in  the  early  spring,  but  is 
very  apt  to  cause  injury  if  the  application  is  made  after  the  time  of 
full  bloom. 

Formula  3 

Zinc  arsenite  powder 3  pounds 

Water 100  gallons 

White  arsenic  (Arsenic  trioxide)  is  only  sparingly  soluble  in  water, 
although  sufficiently  so  to  prohibit  its  use  on  plants  as  an  insecticide. 
Its  use  as  a  stomach  poison  is  therefore  limited  to  the  preparation  of 
poison  baits  for  the  control  of  grasshoppers,  armyworms,  cutworms, 
etc.,  and  in  some  other  cases  where  the  insecticide  is  not  to  be  applied 
to  growing  plants. 

Poison  Bran  Mash. 

Formula  4 

Bran 25  pounds 

White  arsenic 1  pound 

Molasses  (cheap  blackstrap  preferred) 2  quarts 

Mix  the  arsenic  and  the  bran  dry  and  add  the  molasses  which  has 
been  diluted  with  water.  Add  enough  water  and  mix  thoroughly  to 
make  a  dry  mash  which  will  broadcast  easily. 


52  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Citrus  Bran  Mash. 

Formula  5 

White  arsenic  .. - 1  pound 

Molasses  (cheap  blackstrap  preferred) 2  quarts 

Lemons  (or  oranges) - 6  fruits 

Water  (about) 4  gallons 

Bran 25  pounds 

Mix  the  above  materials  as  follows:  Stir  thoroughly  the  white 
arsenic,  molasses,  and  water  first.  Grind  the  lemons,  including  the 
rinds,  in  a  meat  grinder,  or  chop  fine,  and  add  to  this  liquid.  Then 
slowly  pour  this  over  the  bran  and  stir  thoroughly  until  an  even  mix- 
ture is  secured. 

The  amount  of  water  to  use  in  the  preparation  of  these  baits  will 
vary  according  to  the  coarseness  of  the  bran,  or  substitutes.  A  barely 
moist  mash  is  preferable  to  a  wet  one  because  it  does  not  harden  under 
the  heat  of  the  sun  and  remains  palatable,  while  wet  mash  becomes 
baked  and  unattractive. 

Substitutes  in  Poison  Baits. — Paris  green  may  be  substituted  for 
white  arsenic  in  Formulas  4  and  5.  Alfalfa  meal,  shorts,  or  rice  meal 
have  been  successfully  used  as  a  substitute  for  bran  in  the  preparation 
of  the  above  formulas. 

Sodium  Arsenite. — This  arsenical  is  readily  soluble  in  water  and 
is  one  of  the  most  violent  of  the  plant  poisons.  It  probably  acts  more 
quickly  than  any  of  the  better  known  arsenical  poisons,  and  is  com- 
monly used  in  the  preparation  of  weed  killers,  poison  fly-papers,  cattle 
dips  for  the  control  of  ticks,  ant  syrups,  and  to  some  extent  in  the 
preparation  of  poison  baits. 

Sodium  arsenite  may  be  purchased  ready  made  as  a  white  powder, 
but  it  is  not  always  readily  obtained  at  pharmacies,  nor  can  it  always 
be  depended  upon  to  contain  a  uniform  amount  of  arsenic.  This 
chemical  can  be  easily  prepared  from  white  arsenic  by  combining  the 
latter  in  the  presence  of  water  with  sal  soda,  soda  ash,  caustic  soda, 
or  a  good  grade  of  concentrated  lye  in  the  following  proportions : 

Sal  soda  or  washing  soda,  2  parts  to  1  part  of  white  arsenic. 
Soda  ash,  1  part  to  1  part  of  white  arsenic. 
Caustic  soda,  1  part  to  2  parts  of  white  arsenic. 
Concentrated  lye,  1  part  to  2  parts  of  white  arsenic. 

If  sal  soda  or  soda  ash  is  used  it  is  necessary  to  boil  the  mixture 
fifteen  or  twenty  minutes  before  the  arsenic  is  dissolved.  If  caustic 
soda  or  concentrated  lye  is  used,  little  or  no  heat  is  necessary.  In  either 
case,  a  corrosive  chemical  is  formed  known  as  sodium  arsenite. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  53 

A  soluble  arsenical  can  be  made  by  using  one  part  of  caustic  soda 
to  four  parts  of  arsenic  trioxide.  Such  a  solution,  however,  has  a 
tendency  to  form  crystals  on  standing. 

Sodium  Arsenite.  Formula  6 

Sal  soda 2  ounces  (or  2  pounds) 

White  arsenic 1  ounce  (or  1  pound) 

Water  (about)  y2  pint  (or  1  gallon) 

Put  all  the  ingredients  together  in  an  iron  or  graniteware  kettle 
(do  not  use  aluminum)  of  sufficient  size  to  allow  for  considerable 
frothing,  and  boil  fifteen  or  twenty  minutes,  or  until  the  solution  is 
clear. 

A  modification  of  Professor  C.  W.  Woodworth's  formula  which 
has  been  successfully  used  in  municipal  compaigns  against  the  Argen- 
tine ant  is  as  follows : 

Ant  Syrups.  Formula  7 

Strong  for  Weak  for  Argentine  ants 

native  ants  Large  quantity         Small  quantity 

White  arsenic 2  oz.  1  oz.  1  scruple 

Caustic  soda 2  oz.  1  oz.  y>  teaspoonful 

Sugar 1  lb.  20  lbs.  1  lb. 

Water 1  pt.  3  gals.  1  pt. 

For  native  ants,  expose  a  small  quantity  of  the  strong  poison. 

For  the  Argentine  ant,  place  a  sponge  in  a  fruit  jar,  saturate  it 
with  the  weak  poison,  make  a  few  nailholes  in  the  cover  and  keep  jar 
in  pantry  and  several  others  in  the  yard  about  the  house.  Add  more 
poison  from  time  to  time. 

The  U.  S.  Bureau  of  Entomology  recommends  a  later  formula  for 
the  preparation  of  Argentine  ant  syrup  which  is  said  to  be  superior 
to  any  other  formula  tested  by  them,  "on  account  of  its  stability  at 
high  temperatures,  freedom  from  crystalization,  and  continued  attrac- 
tiveness." 

Government  Argentine  Ant  Syrup. 

Formula  8 

Granulated  sugar 9     pounds 

Water 9     pints 

Tartaric  acid  (crystallized)  6     grams 

Benzoate  of  soda 8.4  grams 

Boil  slowly  for  30  minutes.     Allow  to  cool. 

Dissolve  sodium  arsenite  (C.  P.) 15     grams 

In  hot  water y2  pint 

Cool.     Add  poison  solution  to  syrup  and  stir  well. 

Add  to  the  poisoned  syrup : 
Honey    ..,„.„.„ ..„„, 1%  pounds 

Mix  thoroughly. 


54  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

COPPER  COMPOUNDS 

Bordeaux  Mixture  (Average  Strength). 

Formula  9 

Bluestone 16  pounds 

Quicklime • 20  pounds 

Water 200  gallons 

Dissolve  the  bluestone  and  slake  the  lime  in  separate  vats,  the  blue- 
stone  to  be  kept  from  contact  with  all  metals  except  copper.  Thor- 
oughly mix  the  dissolved  bluestone  with  one-half  the  water  and  the 
slaked  lime  with  the  other  half.  Run  the  two  mixtures  together  in  a 
single  stream  into  the  spray  tank  through  a  fine  screen.  For  conven- 
ience, the  mixing  vats  may  be  placed  on  an  elevated  platform,  and  the 
two  parts  mixed  as  they  are  flowing  into  the  spray  tank.  The  milk  of 
lime  should  be  continuously  stirred  during  the  mixing. 

A  somewhat  less  satisfactory  Bordeaux  mixture  may  be  made  as 
follows:  Slake  the  lime  and  dissolve  the  bluestone  in  separate  barrels 
as  above.  Fill  the  spray  tank  half  full  of  water,  add  the  dissolved 
bluestone ;  strain  in  the  slaked  lime  while  the  agitator  is  running ;  add 
remainder  of  water,  and  mix  thoroughly. 

Bordeaux  Paste. 

Formula  10 

A.  Bluestone  12  pounds 

Water 8  gallons 

B.  Quicklime  24  pounds 

Water 8  gallons 

Dissolve  the  bluestone  and  slake  the  lime  separately  in  the  amounts 
of  water  specified.  Then  mix  together  equal  quantities  of  each  ingred- 
ient, making  up  only  enough  for  each  day 's  use. 

Commercial  Bordeaux  Mixture. — Several  preparations  of  this  sort 
are  on  the  market  in  the  form  of  a  paste  or  dry  powder  to  be  diluted 
with  water.  Objection  is  sometimes  made  to  these  preparations  that 
they  will  not  remain  in  suspension  in  water  as  well  as  the  home-made 
Bordeaux  mixture,  but  some  of  them  are  probably  as  good  or  better 
than  the  average  mixture  prepared  on  the  ranch.  The  commercial 
preparations  are  more  expensive,  but  also  more  convenient  for  use,  and 
are  of  especial  value  to  the  small  grower. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  55 

Resin-Bordeaux  Mixture. 

Formula  10a 

Bluestone  20  pounds 

Lime  : 26  pounds 

Resin  10  pounds 

Soap  (soft)  16  pounds 

Water 200  gallons 

Melt  the  resin  in  an  iron  pot,  then  add  the  soft  soap,  heat  and  stir 
until  well  mixed  and  quite  soft.  Add  hot  water  and  boil  and  stir  for 
some  time  until  thoroughly  dissolved.  Add  this  to  the  Bordeaux  which 
has  been  made  in  the  usual  way.  (From  Univ.  Calif.  Exp.  Sta.  Bull. 
165,  p.  77.)  This  is  for  use  on  plants  with  very  smooth  waxy  surfaces 
on  which  fungicides  do  not  spread  and  adhere  well. 

Bluestone  (Copper  Sulfate). — A  soluble  compound  of  copper,  the 
raw  material  for  the  preparation  of  most  other  compounds  of  copper. 
This  cannot  be  used  on  foliage. 

For  dipping  grain  use : 

Formula  11 

Bluestone  ~ 1  pound 

Water 5  gallons 

Dip  for  3  minutes. 

Followed  by : 

Quicklime 1  pound 

Slaked  in  water 10  gallons 

For  lemon  wash  water  use : 

Formula  12 

Bluestone  1%  pounds 

Water  1000  gallons 

SULFUR  AND  SULFUR  COMPOUNDS 

Dry  Sulfur. — For  dusting  upon  plants  for  the  control  of  surface 
mildew,  red  spider,  or  other  parasites  the  fineness  of  the  sulfur  is  an 
all-important  consideration.  Flowers  of  sulfur,  the  finest  and  fluffiest 
grade  of  sublimed  sulfur,  has  been  heretofore  recommended  for  appli- 
cation as  a  dust,  but  at  present  there  are  upon  the  market  several 
brands  of  extremely  finely  ground  sulfurs,  which  are  as  fine  as  some 
of  the  best  grades  of  sublimed  sulfur  and  no  more  expensive.  Some 
of  these  sulfurs,  which  have  been  specially  prepared  for  dusting,  are 
ground  to  pass  a  200-mesh  bolting  cloth.  These  are  apt  to  cake  and 
to  clog  the  dusting  apparatus.  If  three  parts  of  sulfur  are  thoroughly 
mixed  with  one  part  of  hydrated  lime,  kaolin,  or  other  inert  powder, 
these  difficulties  may  be  avoided. 


56  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Sulfur  Pastes  or  Wettable  Sulfurs. — For  various  reasons  it  is  often 
desirable  to  mix  sulfur  and  water  and  apply  to  plants  as  a  spray. 
Sulfur,  however,  is  not  easily  wetted  with  water  and  it  is  a  difficult 
matter  to  make  a  uniform  mixture  of  the  two.  It  has  been  found  that 
a  number  of  substances — soap,  oleic  acid,  glue,  diatomaceous  earth, 
flour,  dextrin,  etc. — when  mixed  with  water  and  sulfur  have  the  prop- 
erty of  counteracting  the  mutual  repulsion  of  sulfur  and  water  with- 
out otherwise  altering  the  nature  of  the  sulfur.  Certain  of  these  sub- 
stances have  been  used  in  the  preparation  of  commercial  sulfur  pastes 
or  wettable  sulfurs.  These  commercial  pastes,  as  now  manufactured, 
contain  from  45  to  50  per  cent  of  sulfur  in  a  very  finely  divided  con- 
dition, the  remainder  being  water  and  one  of  the  substances  mentioned 
above.  The  effect  of  these  pastes  is  that  of  dry  sulfur.  The  usual 
strength  to  use  is: 

Formula  13 

Commercial  sulfur  paste 8  to  21  pounds 

Water  100  gallons 

Home-Made  Wettable  Sulfur. — A  satisfactory  wettable  sulfur  can 
be  easily  made  at  home  by  the  use  of  glue  water  as  follows : 

Formula  14 

Powdered  glue %  ounce 

Hot  water iy2  gallons 

Sulfur  (flowers  or  powdered) 5  pounds 

Water  to  make 100  gallons 

Dissolve  the  glue  in  hot  water  or  soak  over  night  in  one  and  one-half 
gallons  of  cold  water.  Add  the  glue  water  to  the  sulfur  a  little  at  a 
time  and  work  up  into  a  smooth  paste  as  free  from  lumps  as  possible. 
Rubbing  is  better  than  stirring.  Wash  this  paste  into  the  spray  tank 
through  a  fine  screen,  using  the  remainder  of  the  glue  water  to  wash 
it  through  and  a  stiff  brush  to  break  up  the  remainder  of  the  lumps. 
Then  add  plain  water  to  make  100  gallons. 

Another  formula  more  expensive  than  the  above  is : 

Formula  15 
Make  a  paste  of : 

Flour 4  pounds 

Water 4  gallons 

Mix  this  with : 

Sulfur  (sublimed  or  powdered)  5  pounds 

Then  add : 

Water  to  make 100  gallons 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  57 

The  usual  grades  of  sublimed  or  powdered  sulfur  may  be  wetted 
in  the  manner  described  in  Formulas  14  and  15,  but  for  the  best  results 
the  finest  grade  of  sulfur  obtainable  should  be  used.  The  sulfurs 
especially  prepared  for  dusting  are  recommended  for  this  purpose. 

Lime-Sulfur  Solution. — This  is  the  most  active  form  in  which  sulfur 
compounds  are  commonly  used  in  the  control  of  insects  or  fungi.  Its 
causticity  prohibits  its  use  on  any  foliage  except  that  of  the  more  hardy 
plants,  and  then  in  a  very  dilute  form.  Its  principal  use  is  as  a  dor- 
mant spray  for  the  control  of  certain  fungus  diseases,  scale  insects,  and 
a  variety  of  other  pests  of  deciduous  trees. 

Commercial  Lime-Sulfur  Solution. — The  horticulturists  of  the  state 
are  being  supplied  with  concentrated  commercial  lime-sulfur  solution 
of  good  quality  and  at  reasonable  prices.  The  great  bulk  of  this  im- 
portant pest  remedy  used  in  the  state  is  therefore  of  commercial  manu- 
facture, testing  between  32°  and  34°  Baume.  It  is  only  necessary  to 
dilute  this  with  water  before  spraying. 

Home-Made  Lime-Sulfur  Solution. 

Formula  17 

Stone  lime 50  pounds 

Sulfur  (sublimed  or  powdered)  100  pounds 

Water  to  make 50  gallons 

Heat  about  one-third  of  the  total  volume  of  water  required.  When 
the  water  is  hot  add  all  of  the  lime,  and  then  immediately  all  the  sulfur, 
which  should  previously  have  been  made  into  a  thick  paste  with  water. 
After  the  lime  is  slaked  another  third  of  the  water  should  be  added, 
preferably  hot,  and  the  cooking  should  be  continued  until  a  clear 
orange-colored  solution  is  obtained  (usually  45  to  60  minutes),  when 
the  remainder  of  the  water  should  be  added,  either  hot  or  cold,  as  is 
most  convenient.  The  boiling  due  to  the  slaking  of  the  lime  thoroughly 
mixes  the  ingredients  at  the  start,  but  subsequent  stirring  is  necessary 
if  the  wash  is  cooked  by  direct  heat  in  a  kettle.  After  the  wash  has 
been  prepared  it  must  be  allowed  to  settle  and  then  strained  through  a 
fine  sieve  as  it  is  being  run  into  the  spray  tank.  The  resultant  product 
is  a  concentrated  solution  of  lime-sulfur,  which  should  be  diluted  about 
six  times  with  water  for  a  winter  spray. 

Alkali  Sulfides. — Sulfides  of  soda  ("soluble  sulfur")  are  sometimes 
used  in  place  of  lime-sulfur  solution  and  have  some  advantages  over 
the  liquid  preparations. 


58  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

CRUDE  PETROLEUM 

The  use  of  crude  petroleum  is  almost  entirely  limited  to  the  winter 
spraying  of  deciduous  trees  when  the  buds  are  entirely  dormant.  It 
is  generally  applied  from  November  to  February.  The  crude  oil  emul- 
sion is  especially  recommended  for  black  scale  (Sarissetia  oleae),  Euro- 
pean fruit  Lecanium  (Lecanium  corni),  European  or  Italian  pear  scale 
(Epidiaspis  piricola),  cherry  scale  {Lecanium  cerasorum) ,  and  other 
scales  infesting  deciduous  fruit  trees.  It  is  practically  the  only  spray 
treatment  which  has  been  effective  against  the  European  or  Italian 
pear  scale,  and  will  destroy  the  winter  eggs  of  many  of  the  aphids,  of 
the  red  spider,  and  of  some  of  the  defoliating  caterpillars. 

When  crude  oil  is  thoroughly  applied  it  sometimes  penetrates  the 
fruit  buds  to  a  considerable  extent,  and  may  injure  and  even  kill  some 
of  them.  The  great  majority  of  the  buds  are  not  injured,  however, 
but  appear  to  be  stimulated  to  a  more  vigorous  growth,  and  to  the 
production  of  foliage  resistant  to  disease.  It  is  good  practice,  especi- 
ally in  dry  seasons,  not  to  apply  crude  oil  emulsion  until  there  is 
indication  of  swelling  of  the  buds. 

A  natural  crude  petroleum,  testing  about  23°  Baume,  is  preferred, 
as  it  contains  some  of  the  lighter  and  more  penetrating  oils.  Heavier 
crude  oils  have  given  satisfactory  results,  even  those  testing  18°  and 
even  lower.  Kesidium  oils  (the  residue  of  crude  petroleum  after  the 
lighter  portions  have  been  distilled  off)  can  be  used  if  natural  crude 
oil  is  unobtainable,  provided  their  content  of  asphaltum  is  not  too  high 
to  prevent  their  emulsification. 

Crude  Oil  Emulsion. 

Formula  18 

Water 175  gallons 

Liquid  soap 3  gallons 

Natural  crude  petroleum  (21°-24°  Baume) 25  gallons 

Partly  fill  the  spray  tank  with  water,  add  the  liquid  soap,  agitate 
thoroughly,  for  one  minute,  add  crude  oil  and  continue  the  agitation, 
while  running  in  the  remainder  of  the  water.  If  liquid  soap  cannot  be 
obtained,  use  20  pounds  of  fish  oil  soap  dissolved  in  10  gallons  of  boiling 
water  to  which  3  pounds  of  caustic  soda  or  lye  have  been  added.  To 
kill  moss  or  lichens  on  fruit  trees,  add  2  pounds  of  caustic  soda  or  lye 
to  the  formula. 

During  the  spraying  operation  this  emulsion  should  be  thoroughly 
agitated  and  great  care  taken  to  wet  all  of  the  twigs.  From  8  to  10 
gallons  should  be  used  on  a  tree. 


Circular  227]  plant  disease  and  pest  CONTROL  59 

PETROLEUM  DISTILLATES 

Kerosene,  of  about  40°  Baume,  has  been  used  to  a  considerable 
extent  as  an  insecticide,  particularly  on  citrus  trees,  applied  in  the 
form  of  an  emulsion.  The  cheaper,  unrefined  distillates  have  now 
largely  replaced  kerosene  as  a  foliage  spray.  These  are  more  effective 
as  insecticides,  so  that  smaller  percentages  can  be  used  in  the  emulsions, 
but  coupled  with  their  superior  insecticidal  properties  is  their  greater 
toxicity  to  fruit  and  foliage.  The  toxicity  varies  with  climatic  con- 
ditions, foliage  injury  being  most  certain  in  dry  weather  with  a  tem- 
perature of  95°  F.  or  more.  Unfortunately,  the  season  when  spraying 
is  most  effective  against  scale  insects  on  citrus  trees  is  often  during 
the  hottest  and  driest  months.  It  seems  impossible  to  guarantee  im- 
munity from  damage  under  all  conditions  with  any  of  the  distillates 
obtainable. 

Little  injury  to  citrus  fruit  and  foliage  occurs  in  the  coast  regions 
where  distillate  emulsions  have  been  used,  but  in  the  interior  sections 
the  use  of  this  insecticide  is  very  hazardous. 

Spraying  with  distillates,  or  with  any  other  material,  is  not  recom- 
mended as  a  substitute  for  fumigation  in  commercial  citrus  orchards, 
except  in  the  case  of  young  orchards,  trees  about  dooryards,  or  where 
fumigation  may  not  be  convenient,  or  infestation  may  be  light  or 
limited  to  occasional  trees.  In  such  cases,  Formula  19  is  considered 
the  most  satisfactory. 

Kerosene  emulsion  is  the  safest  of  the  petroleum-distillate  sprays, 
although  the  most  expensive.  The  "W.  W."  or  "Water  White"  is  a 
trade  name  of  a  low-grade  kerosene  and  is  safer  than  the  usual  grade 
of  material  sold  as  "distillate."  The  highly  refined  "case  goods" 
kerosene  has  been  found  to  cause  the  least  amount  of  injury  of  any  of 
the  petroleum  derivatives,  but  its  cost  is  prohibitive  except  on  a  small 
scale.  If  much  of  the  keorsene  emulsion  is  allowed  to  run  down  the 
trunks  of  young  trees,  injury  is  likely  to  occur  just  beneath  the  surface 
of  the  ground. 

The  following  formula  is  intended  for  use  on  citrus  trees : 

Kerosene  Emulsion. 

Formula  19 

Kerosene 15  gallons 

Liquid  soap %  gallon 

(Or  hard  soap 4  pounds) 

Water 200  gallons 

If  liquid  soap  is  available,  it  is  preferable  to  hard  soap,  since  no 
heating  is  required.    Hard  soap,  preferably  fish  oil  soap,  is  cut  in  thin 


60  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

slices  and  dissolved  in  hot  water.  The  soap  is  placed  directly  in  the 
spray  tank  with  10  or  15  gallons  of  water  or  more  (the  exact  amount 
is  not  important)  and  the  engine  then  started.  The  oil  is  now  added 
slowly,  and  the  materials  are  emulsified  by  being  run  through  the  pump 
under  pressure.  After  a  few  minutes  the  rest  of  the  water  may  be 
added,  and  the  spray  is  ready  to  be  applied. 

Certain  "tree"  distillates,  testing  31°  to  32°  Baume,  said  to  be 
selected  and  partially  refined,  have  lately  displaced  to  a  considerable 
extent  the  heavier  distillates  of  27°  to  28°  for  use  on  citrus  trees. 

"Tree"  Distillate  Emulsion. 

Formula  20 

Tree  distillate  (31°-32°  Baume)  4  gallons 

Liquid  soap %  gallon 

(Or  hard  soap 5  pounds) 

Water 200  gallons 

These  materials  are  emulsified  in  the  manner  explained  for  the 
kerosene  emulsion,  Formula  19.  If  the  distillate  is  used  without  soap, 
the  following  is  the  formula : 

Straight  "Tree"  Distillate. 

Formula  21 

Tree  distillate  (31°-32°  Baume)  4  to  6  gallons 

Caustic  soda  (95  per  cent) 7  pounds 

Water 200  gallons 

In  the  case  of  the  straight  distillate,  the  oil  is  kept  in  suspension 
in  the  water  by  agitation  and  forms  an  unstable  mechanical  emulsion, 
which  separates  quickly  on  standing.  In  using  this  it  is  necessary  to 
have  the  spray  outfit  equipped  with  a  powerful  and  efficient  agitator, 
which  must  be  kept  going  continuously  during  the  spraying  operations. 

The  use  of  petroleum-distillate  sprays  against  black  scale  on  olive 
trees  is  now  being  recognized  as  profitable.  For  this  purpose  the 
heavier  distillates  of  28°  to  30°  Baume,  being  more  effective,  are  used, 
since  olive  foliage  is  very  resistant  to  spray  injury,  and  also  because 
the  spray  can  be  applied  through  the  winter  months  when  low  temper- 
atures and  high  humidities  are  the  rule. 

Distillates  of  this  density  are  also  much  used  as  a  dormant  spray 
on  deciduous  trees,  although  crude  oil  sprays  are  replacing  distillates 
more  and  more  for  this  purpose. 


Circular  227]  plant  DISEASE  AND  PEST  CONTROL  61 

Heavy  Distillate  Emulsions. — For  use  on  olives,  the  following 
mechanical  emulsion  is  recommended : 

Formula  22 

Distillate  (28°  Baume) 7  gallons 

Caustic  soda  (95  per  cent) 5  to  7  pounds 

Water  to  make 200  gallons 

First  dissolve  the  caustic  soda  in  a  small  amount  of  water  and  add 
to  the  water  in  the  spray  tank ;  begin  the  agitation  and  slowly  add  the 
distillate,  continuing  the  agitation  during  application.  This  spray  will 
also  remove  lichens  or  moss  from  trees. 

If  the  amount  of  crude  oil  is  reduced  from  25  gallons  to  15  gallons 
in  Formula  18,  the  crude  oil  emulsion  may  be  used  on  olive  trees  for 
the  control  of  black  scale. 

For  use  on  dormant  deciduous  trees  the  following  is  recommended : 

Formula  23 

Distillate  (27°-28°  Baume)  20  gallons 

Fish  oil  soap  30  pounds 

Water  to  make 12  gallons 

Dissolve  the  fish  oil  soap  in  water,  heating  it  to  the  boiling  point, 
add  the  distillate,  and  agitate  thoroughly  while  the  solution  is  hot. 
For  use,  add  20  gallons  of  water  to  each  gallon  of  the  above  mixture. 

Commercial  Prepared  Emulsions  and  Miscible  Oils. — Many  grow- 
ers realize  the  difficulty  in  securing  proper  materials  for  home-made 
emulsions  and  the  variability  of  the  home-made  mixtures  even  under 
the  best  conditions.  They  prefer  to  buy  manufactured  products,  especi- 
ally when  only  small  quantities  are  needed,  but  the  commercial  emul- 
sions and  miscible  oils  are  no  more  effective  than  a  good  home-made 
preparation  and  are  only  more  convenient.  These  preparations  are 
on  the  market  in  great  variety,  many  being  sold  under  trade  names. 
Practically  all  grades  of  petroleum  distillates,  as  well  as  crude  petro- 
leum, are  obtainable  in  a  form  ready  to  be  used,  after  simple  dilution 
with  water.  If  these  ready-made  preparations  are  to  be  used,  it  is 
especially  important  to  purchase  only  from  reliable  and  well-known 
manufacturers  or  dealers.  The  commercial  products  in  general  are 
satisfactory  for  use  for  the  purposes  indicated  for  the  above  formulas. 


62  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

The  following  is  recommended  for  the  control  of  thrips : 
Distillate  Emulsion  and  Tobacco  Extract. — Government  formula. 

Formula  24 

The  government  formula  for  the  control  of  pear  thrips  is  the 
following : 

Distillate  emulsion . 10  gallons 

"Black  Leaf  40" 1  pint 

Water  to  make  200  gallons 

When  this  formula  was  first  prepared  there  were  few  commercial 
oil  sprays  on  the  market,  so  that  it  was  necessary  first  to  make  a  dis- 
tillate emulsion  (Formula  23).  In  recent  years  there  have  appeared 
the  miscible  oils,  which  may  be  used  as  follows : 

Formula  24a 

Miscible  oil 5  gallons 

"Black  Leaf  40" 1  pint 

Water  to  make 200  gallons 

These  formulas  are  for  use  against  the  adult  "black  thrips,"  and 
should  be  applied  liberally  as  soon  as  any  considerable  number  of  in- 
sects are  found  upon  the  trees.  Bo  not  fail  to  make  daily  inspections 
after  the  buds  begin  to  swell.  Applications  should  be  repeated  if  neces- 
sary until  the  adults  begin  to  lessen  in  numbers. 

In  case  the  "white  thrips"  appear  in  destructive  numbers  later, 
the  same  formula  may  be  safely  used  if  the  oil  content  is  decreased 
and  the  nicotine  increased  as  follows : 

Fobmula  246 

Distillate  emulsion 6  gallons 

"Black  Leaf  40" 1%  pints 

Water  to  make 200  gallons 

Formula  24c 

Miscible  oil 3  gallons 

"Black  Leaf  40" 1%  P^ts 

Water  to  make 200  gallons 

For  work  with  thrips,  the  greater  force  and  volume  delivery  of  the 
spray  gun  has  rendered  it  superior  to  the  spray  rod,  insuring  not  only 
a  better  but  a  quicker  and  easier  job.  The  loss  in  material  is  more 
than  overcome  by  the  rapidity  and  ease  of  operation. 


Circular  227]  plant  disease  and  pest  control  6H 

The  resin  wash  is  chiefly  used  for  young  and  tender  nursery  stock, 
because  it  does  not  cause  the  injury  often  following  the  application 
of  petroleum  distillates.    The  preparation  is : 

Formula  25 

Resin . 10  pounds 

Caustic  soda  (76  per  cent  to  95  per  cent)  3  pounds 

Fish  oil 1%  pounds 

Water  to  make 50  gallons 

To  a  gallon  of  hot  water  in  an  iron  kettle  add  the  fish  oil  and  the 
resin,  and  heat  until  the  latter  is  softened.  After  first  dissolving  the 
caustic  soda  in  a  small  quantity  of  water  add  it  and  stir  the  mixture 
thoroughly.  After  this  pour  in  enough  water  to  make  50  gallons  of 
spray  material. 

Crude  Carbolic  Acid  Emulsion. — For  citrus  trees. 

Formula  26 

Fish  oil  soap 40  pounds 

Crude  carbolic  acid 5  gallons 

Water  to  make 40  gallons 

Dissolve  the  soap  in  hot  water  completely,  add  the  carbolic  acid 
and  heat  to  the  boiling  point  for  twenty  minutes  (reserve  some  water 
to  add  in  case  the  mixture  begins  to  boil  over).  For  use,  add  20 
gallons  of  water  to  every  gallon  of  the  above  solution.  The  emulsion 
needs  little  or  no  agitation. 

CRUDE  CARBOLIC  ACID  AND  DISTILLATE  EMULSION 

Formula  26a 

Fish  oil  soap  (or  liquid  soap,  5  gallons) 40  pounds 

Crude  carbolic  acid  (25  per  cent) 5  gallons 

Distillate  (27°-28°  Baume)  5  gallons 

Water  to  make 50  gallons 

Prepare  as  with  Formula  26,  adding  the  distillate  after  the  crude 
carbolic  acid.  This  mixture  is  specially  recommended  for  mealybugs 
on  dormant  deciduous  fruit  trees.    Dilute  1  to  20  for  use. 

TOBACCO  PREPARATIONS 

Concentrated  commercial  preparations  of  tobacco  have  almost  en- 
tirely superseded  the  home-made  tobacco  infusions  on  account  of  their 
greater  convenience  and  uniformity.  A  material  containing  40  per 
cent  nicotine  in  the  form  of  nicotine  sulfate  is  recommended  for  the 


64  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

preparation  of  contact  insecticides  containing  nicotine.      The  usual 
formula  is : 

Formula  27 

Tobacco  extract  (nicotine  sulfate,  40  per  cent)  1  pint 

Fish  oil  soap 4  to  5  pounds 

Water 100  to  150  gallons 

For  small  quantities,  use  1  teaspoonful  to  1  gallon  of  water. 

Formula  21a 

Nicotine  sulfate,  40  per  cent 1  pint 

Dry  billboard  paste 2  pounds 

Water 150  gallons 

Make  a  paste  of  the  dry  material  and  add  it  to  the  water  and  nico- 
tine. This  spray  is  intended  for  plants,  like  potatoes,  tomatoes,  etc., 
which  are  sensitive  to  soap  mixtures. 

Tobacco  Dust. — Finely  ground  tobacco  dust  finds  some  use  as  an 
insecticide,  particularly  in  the  control  of  aphids.  Fifty  per  cent  of 
kaolin  or  hydrated  lime  is  sometimes  mixed  with  it  as  a  diluent. 

NICODUST  AND  COMBINATIONS 

Nicodust,  invented  and  named  by  Professor  Ralph  E.  Smith,  is 
composed  of  a  carrying  substance,  like  finely  powdered  kaolin  or  lime, 
treated  with  a  concentrated  solution  of  nicotine  sulfate,  commercially 
known  as  "Blackleaf  40."  The  nicotine  in  such  combination, 
especially  with  lime,  becomes  very  volatile  and  is  quickly  driven  off 
by  heat.  In  this  form  therefore  it  acts  largely  as  a  fumigant,  but  may 
be  effective  as  a  contact  poison  as  well.  As  soon  as  mixed,  the  dust 
should  be  packed  in  air-tight  containers  to  retain  the  nicotine  content. 
The  best  results  in  killing  insects  have  been  secured  when  the  tempera- 
ture is  over  70°  F.,  and  very  poor  results  have  followed  its  use  in  cold 
weather.  The  various  strengths  are  usually  denoted  by  the  amount 
of  "Blackleaf  40"  contained,  as  follows:  2  per  cent  "Blackleaf  40," 
4  per  cent,  5  per  cent,  6  per  cent,  10  per  cent,  etc.  A  statement  of  the 
actual  amount  of  nicotine  is  more  accurate  and  is  required  in  the 
guarantee  of  commercial  preparations. 

The  name  nicodust  does  not  belong  exclusively  to  any  particular 
mixture  or  company,  but  was  originated  as  a  convenient  name  for  all 
mixtures  of  this  sort. 

Arsenate  of  lead  and  sulfur  are  mixed  with  nicodust  at  the  time  of 
manufacture  and  give  convenient  combinations  for  treating  different 


Circular  227]  plant  disease  and  pest  control  65 

types  of  insects  or  insects  and  fungus  diseases  at  one  application. 
Sulfur-nicodust,  under  actual  field  tests,  appears  to  be  more  efficient 
in  killing  insects  than  ordinary  nicodust  containing  the  same  percent- 
age of  "Blackleaf  40."  Thus  in  the  control  of  the  rosy  apple  aphis, 
a  sulfur-nicodust  containing  50  per  cent  of  sulfur,  6  per  cent  of 
"Blackleaf  40,"  and  44  per  cent  of  inert  material  gave  far  better 
results  than  a  6  per  cent  nicodust. 

The  strengths  commonly  used  are  2  per  cent  nicodust  for  walnut 
aphis  and  cherry  or  pear  slug,  5  or  6  per  cent  for  most  of  the  aphids, 
thrips,  etc.,  and  a  10  per  cent  dust  for  the  more  resistant  aphids  such 
as  the  pea  aphis.  Nearly  all  of  the  hairy  caterpillars,  such  as  the  tent 
caterpillars,  webworms,  thistle  butterfly  larvae,  as  well  as  the  velvety 
cabbage  worms,  to  which  the  nicodust  adheres  readily,  are  easily  killed 
with  a  6  per  cent  dust  if  applied  while  the  caterpillars  are  quite  young. 
Smooth  caterpillars,  like  cutworms,  on  the  other  hand,  do  not  readily 
succumb  to  any  ordinary  treatment  with  the  material.  Insects  which 
are  protected  with  a  waxy  or  cottony  material,  like  the  woolly  apple 
aphis,  the  mealy  plum  louse,  mealybugs,  etc.,  are  not  susceptible  to 
nicodust  at  all,  while  those  which  have  a  wet  or  slimy  covering,  like 
the  cherry  or  pear  slug,  or  glandular  hairs,  like  the  walnut  aphis,  are 
easily  killed  with  very  weak  nicotine  contents. 


MISCELLANEOUS 

Corrosive  Sublimate  (Bichloride  of  Mercury). — This  is  a  very 
poisonous  substance  and  is  one  of  the  most  powerful  of  germicides; 
it  is  employed  to  some  extent  in  plant  disease  treatment.  The  usual 
strength  is : 

Formula  28 

Corrosive  sublimate 1  ounce 

Water 8  gallons 

Or  1  part  to  1000. 

Tablets  to  make  this  strength  when  added  to  1  pint  of  water  may 
be  obtained  at  drug  stores.  Distilled  or  rain  water  should  be  used; 
the  solution  must  not  be  kept  in  a  metal  container.  It  is  also  quickly 
spoiled  by  contact  with  clay  or  an  organic  substance  such  as  the  cut 
surface  of  potatoes. 

Another  formula  is  recommended  by  Mr.  C.  F.  Reimer  for  dis- 
infecting tools  and  cuts  in  pear  blight  control  work.  It  will  probably 
be  found  superior  to  Formula  28  for  general  tree  work  of  this  kind. 


66  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

It  is: 

Formula  28a 

Mercuric  chloride 1  ounce 

Mercuric  cyanide 1  ounce 

Water 4  gallons 

Or  1  part  of  each  ingredient  to  500. 

Whitewash. 

Formula  29 
(Ordinary  Formula) 

Water .. 2  gallons 

Quicklime 10  pounds 

Add  more  water  after  slaking  to  bring  the  wash  to  the  desired 
consistency. 

A  more  durable  whitewash : 

Formula  30 

Quicklime 5  pounds 

Salt i/o  pound 

Sulfur %  pound 

Slake  the  lime  slowly  with  water  and  add  the  salt  and  sulfur  while 
it  is  boiling.  Add  enough  more  water  to  make  a  good  wash.  This  is 
good  for  whitewashing  the  bodies  of  trees  in  the  fall.  In  localities 
where  there  are  deer  this  whitewash  is  not  recommended,  as  the  deer 
are  said  to  be  attracted  by  the  salt  it  contains  and  injure  the  trees. 

Government  Whitewash. 

Formula  31 

Quicklime 40  pounds 

Salt - 15  pounds 

Rice  flour 3  pounds 

Spanish  whiting i/2  pound 

Glue - 1  pound 

Water 5  gallons 

Grafting  Wax. — Many  different  combinations  are  used  for  this 
purpose,  most  of  them  being  various  combinations  of  beeswax  and  resin. 
The  following  formula  is  a  good  one : 

Formula  32 

Resin 4  pounds 

Beeswax 1  pound 

Linseed  oil  1  pint 

The  ingredients  are  all  melted  and  mixed  together  in  a  kettle.  In 
hot  weather  use  more  resin. 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  67 

Some  use  one  pound  of  tallow  as  a  substitute  for  the  linseed  oil. 
One  ounce  of  lampblack  or  one  pint  of  flour  is  sometimes  added. 
Asphaltum  is  used  to  some  extent  as  a  substitute  for  resin  and  bees- 
wax, and,  in  fact,  straight  asphaltum  is  used  successfully  in  some  cases 
for  grafting  wax. 

Carbon  Bisulfide. — A  liquid  which  evaporates  quickly  when  ex- 
posed to  the  air,  forming  a  heavy  and  inflammable  vapor  of  great 
penetrating  power.  In  using  the  material  for  fumigation,  it  is  essen- 
tial that  it  be  placed  near  the  top  of  the  room  in  a  shallow  container 
in  order  that  the  heavy  vapors  as  they  are  given  off  may  thoroughly 
diffuse  through  the  air  contained  in  the  space  to  be  fumigated.  The 
proper  amount  to  use  depends  upon  the  type  of  room  being  fumigated 
and  ranges  from  10  pounds  to  about  30  pounds  to  1000  cubic  feet  in 
ordinary  rooms  where  the  walls  and  floor  have  not  been  made  especially 
tight.  The  best  results  are  obtained  by  doing  this  work  when  the 
temperature  is  above  70°  F. 

Carbon  bisulfide  is  one  of  the  best  agents  for  destroying  ground 
squirrels  that  have  failed  to  take  poisoned  grain,  or  having  once  sur- 
vived the  poison  refuse  to  take  it  again.  It  is  most  effective  if  used 
during  the  winter  season  when  the  ground  is  wet.  The  best  methods 
of  applying  it  are  by  the  use  of  the  "waste-ball"  and  of  the  "de- 
structor." The  common  waste-ball  method  is  to  pour  a  tablespoonful 
of  carbon  bisulfide  on  a  piece  of  cotton  waste,  corncob,  horse  manure, 
or  other  absorptive  material,  and  then  to  throw  this  as  far  down  the 
hole  as  possible,  closing  the  opening  immediately  with  earth.  Ex- 
ploding the  gas  with  a  torch  before  closing  the  opening  is  recommended 
where  the  ground  is  damp  and  there  is  no  danger  of  fire.  The  ex- 
plosion of  the  gas  forms  new  compounds  which  are  poisonous  and  may 
diffuse  somewhat  more  rapidly  than  the  vapors  of  the  material.  The 
"destructor"  pumps  the  vaporized  carbon  bisulfide  into  the  burrow, 
and  is  said  to  be  as  effective  as  exploding  the  gas. 

Poisoned  Barley. — Below  is  the  latest  government  formula  for 
preparing  poisoned  barley  for  California  ground  squirrels: 

Formula  33 

Barley  (clean  grain)  16  quarts 

Strychnin  (powdered  alkaloid)  1  ounce 

Bicarbonate  of  soda  (baking  soda) 1  ounce 

Thin  starch  paste %  pint 

Heavy  corn  syrup 14  pint 

Glycerin 1  tablespoonful 

Saccharin  X 


10 


ounce 


68  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Mix  thoroughly  1  ounce  of  powdered  strychnin  and  1  ounce  of 
common  baking  soda.  Stir  this  into  three-quarters  pint  of  thin,  hot 
starch  paste  and  stir  to  a  creamy  mass.  (The  starch  paste  is  made 
by  dissolving  1  heaping  teaspoonful  of  dry  starch  in  a  little  cold  water, 
and  then  adding  it  to  three-quarters  pint  of  boiling  water;  boil  and 
stir  constantly  until  a  thin  clear  paste  is  formed.)  Add  one-quarter 
pint  of  heavy  corn  syrup  and  1  tablespoonful  of  glycerin  and  stir 
thoroughly.  Add  one-tenth  ounce  of  saccharin  and  stir  thoroughly. 
Pour  this  mixture  over  16  quarts  of  clean  barley  and  mix  well  so  that 
each  grain  is  coated. 

Caution. — All  containers  of  poison  and  all  utensils  used  in  the 
preparation  of  poisons  should  be  kept  plainly  labeled  and  out  of  reach 
of  children,  irresponsible  persons,  and  live  stock. 

SPREADERS 

Spreaders  are  often  added  to  sprays  to  give  them  a  more  even  dis- 
tribution over  the  surface  of  the  leaves  and  to  prevent  them  from  col- 
lecting into  drops.  Some  of  them  also  have  insecticidal  value  and 
others  act  as  adhesives.  So  much  is  claimed  for  these  materials  which 
is  not  fully  warranted  that  many  persons  have  come  to  feel  that  none 
should  be  recommended.  However,  the  advantages  gained  should  not 
be  entirely  overlooked,  and  we  include  here  some  of  the  more  important 
substances  used  for  these  purposes. 

Casein. — This  is  a  comparatively  new  material  for  use  as  a  spreader 
and  adhesive  in  sprays.  It  is  a  dry  product  which  readily  mixes  in 
cold  water  and  is  put  up  in  small  or  large  containers.  One  and  one- 
half  pounds  are  sufficient  for  200  gallons  of  the  diluted  spray.  Casein 
is  soluble  only  in  alkaline  solutions  and  is  therefore  worthless  in  acid 
insecticides  and  fungicides  which  are,  however,  seldom  used. 

Flour  Paste,  Billboard  Paste. — These  materials  are  excellent 
spreaders  and  act  as  adhesives  as  well.  They  may  be  used  with  safety 
in  all  sprays,  because  they  give  no  chemical  reactions.  Flour  paste 
and  certain  of  the  dry  billboard  and  paperhanger  ?s  pastes  should  be 
mixed  in  a  small  quantity  of  hot  water  before  adding  to  the  spray 
tank,  and  are  somewhat  difficult  to  handle.  A  specially  prepared  bill- 
board and  paperhanger 's  paste,  known  as  "steamed  paste,"  is  already 
cooked,  and  as  a  wet  paste  mixes  readily  with  cold  water.  It  may  be 
obtained  in  barrel  lots  or  in  small  quantities  from  paint  and  paper 
dealers.    The  amounts  to  be  used  are  as  follows : 


Circular  227]  PLANT  DISEASE  AND  PEST  CONTROL  G9 

Flour  (cheap  grade),  2  to  4  pounds  to  200  gallons  of  dilute  spray 
material. 

Dry  billboard  paste,  2  pounds  to  200  gallons  of  dilute  spray  ma- 
terial. 

Steamed  paste,  4  pounds  to  200  gallons  of  dilute  spray  material. 

Glue. — As  a  spreader  and  adhesive,  glue  has  long  been  used  in 
sprays,  and,  like  the  flour  pastes,  may  be  used  in  all  kinds  of  materials. 
Two  ounces  of  dry  glue  dissolved  in  hot  water  are  sufficient  for  200 
gallons  of  diluted  sprays. 

Oil  Emulsions  and  Miscible  Oils. — Because  of  their  penetration, 
these  materials  are  often  of  value  in  carrying  other  materials,  like 
nicotine.  They  should  be  used  sparingly,  about  2  gallons  to  200  gallons 
of  diluted  spraying  materials.  When  so  diluted  they  have  little  value 
except  as  spreaders. 

Resin-fish  oil  soap  (see  Formula  10a)  is  often  used  with  Bordeaux 
mixture.  It  is  somewhat  tedious  to  prepare  and  may  now  be  purchased 
ready  to  use.  This  is  very  similar  in  character  to  the  resin  wash  (see 
Formula  25). 

Soap. — This  is  one  of  the  oldest  and  best  known  spreaders  and  is 
often  used  in  sprays  for  this  purpose  as  well  as  for  an  emulsifier  and 
insecticide.  As  a  spreader  for  such  materials  as  arsenate  of  lead,  for 
codling  moth,  use  5  pounds  fish  oil  soap  to  200  gallons  of  diluted  spray 
material. 


V 


STATION  PUBLICATIONS  AVAILABLE  FOR  FREE  DISTRIBUTION 

BULLETINS 


No. 
185. 

241. 
246. 
251. 


253. 

261. 
262. 

263. 
266. 

267. 
268. 
270. 


271. 
273. 

275. 

276. 
278. 
279. 
280. 

282. 

283. 
285. 
286. 
290. 

294. 
297. 
298. 
299. 
300. 
301. 


Report  of  Progress  in  Cereal  Investiga- 
tions. 

Vine  Pruning  in  California,  Part  I. 

Vine  Pruning  in  California,  Part  II. 

Utilization  of  the  Nitrogen  and  Organic 
Matter  in  Septio  and  Imhoff  Tank 
Sludges. 

Irrigation  and  Soil  Conditions  in  the 
Sierra  Nevada  Foothills,  California. 

Melaxuma  of  the  Walnut,  "Juglans  regia." 

Citrus  Diseases  of  Florida  and  Cuba 
Compared  with  Those  of  California. 

Size  Grades  for  Ripe  Olives. 

A  Spotting  of  Citrus  Fruits  Due  to  the 
Action  of  Oil  Liberated  from  the  Rind. 

Experiments  with  Stocks  for  Citrus. 

Growing  and  Grafting  Olive  Seedlings. 

A  Comparison  of  Annual  Cropping,  Bi- 
ennial Cropping,  and  Green  Manures 
on  the  Yield  of  Wheat. 

Feeding  Dairy  Calves  in  California. 

Preliminary  Report  on  Kearney  Vineyard 
Experimental  Drain. 

The  Cultivation  of  Belladonna  in  Cali- 
fornia. 

The  Pomegranate. 

Grain  Sorghums. 

Irrigation  of  Rice  in  California. 

Irrigation  of  Alfalfa  in  the  Sacramento 
Valley. 

Trials  with  California  Silage  Crops  for 
Dairy  Cows. 

The  Olive  Insects  of  California. 

The  Milk  Goat  in  California. 

Commercial  Fertilizers. 

The  June  Drop  of  Washington  Navel 
Oranges. 

Bean  Culture  in  California. 

The  Almond  in  California. 

Seedless  Raisin  Grapes. 

The  Use  of  Lumber  on  California  Farms. 

Commercial  Fertilizers. 

California  State  Dairy  Cow  Competition, 
1916-1918. 


No. 
302 


Control  of  Ground  Squirrels  by  the  Fumi- 
gation Method. 

A  Study  on  the  Effects  of  Freezes  on 
Citrus  in  California. 

I.  Fumigation  with  Liquid  Hydrocyanic 
Acid.  II.  Physical  and  Chemical  Pro- 
perties of  Liquid  Hydrocyanic  Acid. 

I.  The  Carob  in  California.  II.  Nutritive 
Value  of  the  Carob  Bean. 

Plum  Pollination. 

Mariout  Barley. 

Pruning  Young  Deciduous  Fruit  Trees. 

The  Kaki  or  Oriental  Persimmon. 

Selections  of  Stocks  in  Citrus  Propagation. 

The  Effects  of  Alkali  on  Citrus  Trees. 

Control  of  the  Coyote  in  California. 

Commercial  Production  of  Grape  Syrup. 

The  Evaporation  of  Grapes. 

Heavy  vs.  Light  Grain  Feeding  for  Dairy 
Cows. 

Storage  of  Perishable  Fruit  at  Freezing 
Temperatures. 

Rice    Irrigation    Measurements   and   Ex- 
periments in  Sacramento  Valley,  1914- 
1919. 
326.  Brown  Rot  of  Apricots. 

328.  Prune  Growing  in  California. 

329.  A  White  Fir  Volume  Table. 

330.  Dehydration  of  Fruits. 

331.  Phylloxera-Resistant  Stocks. 

332.  Walnut  Culture  in  California. 

333.  Some   Factors   Affecting   the   Quality   of 

Ripe   Olives   Sterilized   at   High   Tem- 
peratures. 

334.  Preliminary  Volume  Tables  for  Second- 

Growth  Redwoods. 

335.  Cocoanut  Meal  as  a  Feed  for  Dairy  Cows 

and  Other  Livestock. 

336.  The  Preparation  of  Nicotine  Dust  as  an 

Insecticide. 

337.  Some  Factors  of  Dehydrater  Efficiency. 


304. 
308. 


309. 

310. 
312. 
313. 
316. 
317. 
318. 
320. 
321. 
322. 
323. 

324. 

325. 


CIRCULARS 


No.  No. 

70.  Observations    on    the    Status    of    Corn  155. 

Growing  in  California.  157. 

76.  Hot  Room  Callusing.  153. 

82.  The  Common  Ground  Squirrels  of  Cali-  159. 

fornia.  160. 

87.  Alfalfa.  161. 

110.  Green  Manuring  in  California.  164. 

111.  The  Use  of  Lime  and  Gypsum  on  Cali-  165. 

fornia  Soils. 

113.  Correspondence  Courses  in  Agriculture.  166. 

114.  Increasing  the  Duty  of  Water.  167. 

115.  Grafting  Vinifera  Vineyards.  168. 

126.  Spraying  for  the  Grape  Leaf  Hopper. 

127.  House  Fumigation.  169. 

128.  Insecticide  Formulas.  170. 

129.  The  Control  of  Citrus  Insects. 

130.  Cabbage  Growing  in  California.  172. 
135.  Official  Tests  of  Dairy  Cows.  173. 

138.  The  Silo  in  California  Agriculture.  174. 

139.  The  Generation  of  Hydrocyanic  Acid  Gas  175. 

in  Fumigation  by  Portable  Machines. 

144.  Oidium  or  Powdery  Mildew  of  the  Vine.  176. 
148.  "Lungworms." 

151.  Feeding  and  Management  of  Hogs.  177. 

152.  Some  Observations  on  the  Bulk  Handling  178. 

of  Grain  in  California.  179. 

153.  Announcement    of    the    California    State 

Dairy  Cow  Competition,  1916-18.  181. 

154.  Irrigation    Practice    in    Growing    Small  182. 

Fruits  in  California. 


Bovine  Tuberculosis. 

Control  of  the  Pear  Scab. 

Home  and  Farm  Canning. 

Agriculture  in  the  Imperial  Valley. 

Lettuce  Growing  in  California. 

Potatoes  in  California. 

Small  Fruit  Culture  in  California. 

Fundamentals    of    Sugar    Beet    Culture 

under  California  Conditions. 
The  County  Farm  Bureau. 
Feeding  Stuffs  of  Minor  Importance. 
Spraying  for  the  Control  of  Wild  Morning- 

Glory  within  the  Fog  Belt. 
The  1918  Grain  Crop. 
Fertilizing  California  Soils  for  the   1918 

Crop. 
Wheat  Culture. 

The  Construction  of  the  Wood-Hoop  Silo. 
Farm  Drainage  Methods. 
Progress  Report  on  the  Marketing  and 

Distribution  of  Milk. 
Hog  Cholera  Prevention  and  the  Serum 

Treatment. 
Grain  Sorghums. 

The  Packing  of  Apples  in  California. 
Factors  of  Importance  in  Producing  Milk 

of  Low  Bacterial  Count. 
Control  of  the  California  Ground  Squirrel. 
Extending  the  Area  of  Irrigated  Wheat  in 

California  for  1918. 


CIRCULARS — Continued 


No. 

183.  Infectious  Abortion  in  Cows. 

184.  A  Flock  of  Sheep  on  the  Farm. 

185.  Beekeeping  for  the  Fruit-grower  and  Small 

Rancher  or  Amateur. 

188.  Lambing  Sheds. 

189.  Winter  Forage  Crops. 

190.  Agriculture  Clubs  in  California. 

191.  Pruning  the  Seedless  Grapes. 

193.  A  Study  of  Farm  Labor  in  California. 
198.  Syrup  from  Sweet  Sorghum. 

201.  Helpful  Hints  to  Hog  Raisers. 

202.  County  Organizations  for  Rural  Fire  Con- 

trol. 

203.  Peat  as  a  Manure  Substitute. 

205.  Blackleg. 

206.  Jack  Cheese. 

208.  Summary  of  the  Annual  Reports  of  the 

Farm  Advisors  of  California. 

209.  The  Function  of  the  Farm  Bureau. 

210.  Suggestions  to  the  Settler  in  California. 


No. 

214. 


Seed   Treatment   for   the   Prevention   of 

Cereal  Smuts. 
Feeding  Dairy  Cows  in  California. 
Methods    for    Marketing    Vegetables    in 

California. 
Advanced  Registry  Testing  of  Dairy  Cows. 

219.  The  Present  Status  of  Alkali. 

220.  Unfermented  Fruit  Juices. 

221.  How  California  is   Helping  People  Own 
Farms  and  Rural  Homes. 

Fundamental  Principles   of  Co-operation 

in  Agriculture 
The  Pear  Thrips. 
Control  of  the  Brown  Apricot  Scale  and 

the    Italian   Pear    Scale   on    Deciduous 

Fruit  Trees. 

226.  Protection  of  Vineyards  from  Phylloxera. 

227.  Plant  Disease  and  Pest  Control. 

228.  Vineyard  Irrigation  in  Arid  Climates. 

229.  Cordon  Pruning. 


215. 
217. 


218. 


222. 


223 
224. 


